diff --git a/apps/web/src/components/brand/tessera-logo.tsx b/apps/web/src/components/brand/tessera-logo.tsx
index db8519f..e27a175 100644
--- a/apps/web/src/components/brand/tessera-logo.tsx
+++ b/apps/web/src/components/brand/tessera-logo.tsx
@@ -20,9 +20,10 @@ export interface TesseraLogoProps {
    * Schaltet die halbtransparente helle Kontur der Grundplatte im dunklen
    * Erscheinungsbild ein. Auf Flaechen, die unabhaengig vom
    * Erscheinungsbild immer hell sind (etwa das gelbe Anmelde-Panel), muss
-   * dies auf `false` gesetzt werden. Vorgabe: `true`.
+   * dies auf `false` gesetzt werden; auf immer dunklen Flaechen (App-Leiste,
+   * Anmelde-Panel) auf `'always'`. Vorgabe: `true`.
    */
-  plateOutline?: boolean;
+  plateOutline?: boolean | 'always';
   /** Zusaetzliche Klassen fuer das aeusserste Element der gewaehlten Variante. */
   className?: string;
   /** Zusaetzliche Klassen fuer den Schriftzug (nur `horizontal`). */
@@ -38,7 +39,7 @@ function LogoMark({
   ariaLabel,
 }: {
   size: number;
-  plateOutline: boolean;
+  plateOutline: boolean | 'always';
   className?: string;
   ariaLabel: string;
 }) {
@@ -61,9 +62,11 @@ function LogoMark({
         fill={BRAND_PLATE}
         strokeWidth={2}
         className={
-          plateOutline
-            ? 'stroke-transparent dark:stroke-white/25'
-            : 'stroke-transparent'
+          plateOutline === 'always'
+            ? 'stroke-white/20'
+            : plateOutline
+              ? 'stroke-transparent dark:stroke-white/25'
+              : 'stroke-transparent'
         }
       />
       {/*
diff --git a/apps/web/src/components/bug-report/bug-report-button.tsx b/apps/web/src/components/bug-report/bug-report-button.tsx
index b9cc8d8..9901366 100644
--- a/apps/web/src/components/bug-report/bug-report-button.tsx
+++ b/apps/web/src/components/bug-report/bug-report-button.tsx
@@ -34,7 +34,7 @@ export function BugReportButton() {
       <button
         type="button"
         onClick={handleClick}
-        className="inline-flex items-center justify-center rounded-md p-2 text-muted-foreground hover:bg-muted hover:text-foreground transition-colors disabled:opacity-50"
+        className="inline-flex h-8 w-8 items-center justify-center rounded-md text-appbar-muted hover:bg-appbar-hover hover:text-appbar-foreground transition-colors disabled:opacity-50 focus-visible:outline-2 focus-visible:outline-offset-[-2px] focus-visible:outline-appbar-foreground"
         aria-label={t('button')}
         title={t('button')}
         disabled={capturing}
diff --git a/apps/web/src/components/dashboard/dashboard-tabs.tsx b/apps/web/src/components/dashboard/dashboard-tabs.tsx
index bdbde39..a66068e 100644
--- a/apps/web/src/components/dashboard/dashboard-tabs.tsx
+++ b/apps/web/src/components/dashboard/dashboard-tabs.tsx
@@ -312,18 +312,20 @@ export function DashboardTabs({
   const bar = (
     <nav
       aria-label={t('tabs.navLabel')}
-      className="flex min-w-0 max-w-full items-center gap-1.5"
+      className="flex h-[var(--header-height)] min-w-0 max-w-full items-center gap-1.5"
       title={dashboards.length > 1 ? t('tabs.dragHint') : undefined}
     >
-      {/* Eingelassene Spur (32 px): der aktive Reiter liegt erhaben darauf. */}
-      <div className="h-8 min-w-0 max-w-full rounded-lg bg-muted p-0.5 shadow-[inset_0_1px_2px_oklch(0_0_0/0.08)] md:max-w-[min(56vw,720px)]">
+      {/* Reiter im Fluent-Stil auf der dunklen App-Leiste (Design „Mosaik“):
+          volle Leistenhoehe, der aktive Reiter weiss und halbfett mit 2 px
+          Akzentlinie an der Unterkante der Leiste. */}
+      <div className="h-[var(--header-height)] min-w-0 max-w-full md:max-w-[min(56vw,720px)]">
         <div
           ref={scrollRef}
           role="tablist"
           aria-describedby={dashboards.length > 1 ? hintId : undefined}
           onScroll={measureOverflow}
           style={maskStyle}
-          className="flex h-7 items-center gap-0.5 overflow-x-auto [scrollbar-width:none] [&::-webkit-scrollbar]:hidden"
+          className="flex h-full items-stretch gap-0.5 overflow-x-auto [scrollbar-width:none] [&::-webkit-scrollbar]:hidden"
         >
           {orderedTabs.map((tab, index) => {
             const isActive = tab.id === activeDashboardId;
@@ -339,16 +341,22 @@ export function DashboardTabs({
                 }}
                 data-tab-index={index}
                 data-testid={`dashboard-tab-${tab.id}`}
-                className={`flex h-7 shrink-0 touch-none items-center rounded-md transition-colors ${
+                className={`relative flex shrink-0 touch-none items-center transition-colors ${
                   isActive
-                    ? 'bg-card text-foreground shadow-sm'
-                    : 'text-muted-foreground hover:bg-card/60 hover:text-foreground'
+                    ? 'text-appbar-foreground'
+                    : 'text-appbar-muted hover:text-appbar-foreground'
                 }`}
                 onPointerDown={(e) => handlePointerDown(e, tab.id)}
                 onPointerMove={handlePointerMove}
                 onPointerUp={handlePointerUp}
                 onPointerCancel={handlePointerCancel}
               >
+                {isActive && (
+                  <span
+                    aria-hidden="true"
+                    className="pointer-events-none absolute inset-x-3 bottom-0 h-[2px] rounded-full bg-primary"
+                  />
+                )}
                 {isRenaming ? (
                   <input
                     ref={renameInputRef}
@@ -366,7 +374,7 @@ export function DashboardTabs({
                     }}
                     maxLength={40}
                     aria-label={t('tabs.renameInputLabel')}
-                    className="h-6 w-32 rounded border border-border bg-background px-2 text-sm text-foreground"
+                    className="h-7 w-32 rounded-md border border-white/25 bg-white/10 px-2 text-sm text-appbar-foreground outline-none focus:border-primary"
                   />
                 ) : (
                   <button
@@ -380,8 +388,9 @@ export function DashboardTabs({
                     tabIndex={isFocusable ? 0 : -1}
                     onClick={() => handleTabClick(tab.id)}
                     onKeyDown={(e) => handleTabKeyDown(e, index)}
-                    className={`h-7 cursor-grab whitespace-nowrap rounded-md px-3 text-sm focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring ${
-                      isActive ? 'font-medium' : ''
+                    data-text={tab.name}
+                    className={`inline-flex h-8 cursor-grab flex-col items-center justify-center whitespace-nowrap rounded-md px-3 text-sm transition-colors hover:bg-appbar-hover focus-visible:outline-2 focus-visible:outline-offset-[-2px] focus-visible:outline-appbar-foreground after:invisible after:h-0 after:overflow-hidden after:font-semibold after:content-[attr(data-text)] ${
+                      isActive ? 'font-semibold' : ''
                     }`}
                   >
                     {tab.name}
@@ -394,7 +403,7 @@ export function DashboardTabs({
                     onClick={() => startRename(tab)}
                     aria-label={t('tabs.renameButtonLabel')}
                     title={t('tabs.renameButtonLabel')}
-                    className="-ml-1.5 rounded p-1 text-muted-foreground hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring"
+                    className="-ml-1.5 rounded p-1 text-appbar-muted hover:text-appbar-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-appbar-foreground"
                   >
                     <svg
                       aria-hidden="true"
@@ -419,7 +428,7 @@ export function DashboardTabs({
                     onClick={() => setPendingDeleteId(tab.id)}
                     aria-label={t('tabs.deleteButtonLabel')}
                     title={t('tabs.deleteButtonLabel')}
-                    className={`${isEditMode && isActive ? '' : '-ml-1.5'} mr-1 rounded p-1 text-muted-foreground hover:text-destructive focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring`}
+                    className={`${isEditMode && isActive ? '' : '-ml-1.5'} mr-1 rounded p-1 text-appbar-muted hover:text-red-300 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-appbar-foreground`}
                   >
                     <svg
                       aria-hidden="true"
@@ -453,7 +462,7 @@ export function DashboardTabs({
           onClick={onCreate}
           aria-label={t('tabs.add')}
           title={t('tabs.add')}
-          className="flex h-7 w-7 shrink-0 items-center justify-center rounded-full border border-border bg-card text-muted-foreground shadow-sm transition-colors hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring"
+          className="flex h-7 w-7 shrink-0 items-center justify-center rounded-md border border-white/20 text-appbar-muted transition-colors hover:bg-appbar-hover hover:text-appbar-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-appbar-foreground"
         >
           <svg
             aria-hidden="true"
@@ -510,7 +519,7 @@ export function DashboardTabs({
               <button
                 type="button"
                 onClick={() => setPendingDeleteId(null)}
-                className="rounded border border-border px-4 py-2 text-sm text-foreground transition-colors hover:bg-muted"
+                className="btn btn-secondary"
               >
                 {tCommon('cancel')}
               </button>
diff --git a/apps/web/src/components/layout/header.test.tsx b/apps/web/src/components/layout/header.test.tsx
index 675d951..e99e1e3 100644
--- a/apps/web/src/components/layout/header.test.tsx
+++ b/apps/web/src/components/layout/header.test.tsx
@@ -1,6 +1,7 @@
 import { cleanup, render, screen, waitFor } from '@testing-library/react';
 import { afterEach, describe, expect, it, vi } from 'vitest';
 import { useAuthStore } from '@/lib/stores/auth-store';
+import { useNavStore } from '@/lib/stores/nav-store';
 
 /**
  * header.test — Sitzungswaechter im Header (quick-260917-gyd).
@@ -166,15 +167,35 @@ describe('Header — Mitte der Kopfzeile (quick-260924-h7x)', () => {
     await waitFor(() => expect(fetchSessionState).toHaveBeenCalled());
   });
 
-  it('auf anderen Seiten: „Startseite“ bleibt wie bisher', async () => {
-    mockPathname = '/modules/proxmox';
-    vi.stubGlobal('location', { href: '', pathname: '/modules/proxmox', search: '' });
+  it('auf anderen Seiten: Name der aktuellen Seite statt „Startseite“ (Design „Mosaik“)', async () => {
+    mockPathname = '/marketplace';
+    vi.stubGlobal('location', { href: '', pathname: '/marketplace', search: '' });
     fetchSessionState.mockResolvedValue({ status: 'unavailable' });
 
     await renderHeader();
 
-    expect(screen.getByText('Startseite')).toBeInTheDocument();
+    expect(screen.getByText('Marktplatz')).toBeInTheDocument();
+    expect(screen.queryByText('Startseite')).not.toBeInTheDocument();
     expect(document.getElementById('header-center-slot')).not.toBeNull();
     await waitFor(() => expect(fetchSessionState).toHaveBeenCalled());
   });
+
+  it('auf Modulseiten: Modulname aus der Seitenleiste, sonst der Ersatztitel', async () => {
+    mockPathname = '/modules/infrastructure/proxmox';
+    vi.stubGlobal('location', { href: '', pathname: mockPathname, search: '' });
+    fetchSessionState.mockResolvedValue({ status: 'unavailable' });
+
+    await renderHeader();
+    // Noch keine Module geladen: Ersatztitel aus den Uebersetzungen.
+    expect(screen.getByText('Proxmox')).toBeInTheDocument();
+
+    cleanup();
+    useNavStore.getState().setModules([
+      { id: 'm1', slug: 'proxmox', name: 'Proxmox-Monitor', category: 'infrastructure' },
+    ]);
+    await renderHeader();
+    expect(screen.getByText('Proxmox-Monitor')).toBeInTheDocument();
+    useNavStore.getState().setModules([]);
+    await waitFor(() => expect(fetchSessionState).toHaveBeenCalled());
+  });
 });
diff --git a/apps/web/src/components/layout/header.tsx b/apps/web/src/components/layout/header.tsx
index 145f605..70bfdaf 100644
--- a/apps/web/src/components/layout/header.tsx
+++ b/apps/web/src/components/layout/header.tsx
@@ -12,6 +12,7 @@ import { ThemeToggle } from '@/components/theme-toggle';
 import { BugReportButton } from '@/components/bug-report/bug-report-button';
 import { HEADER_CENTER_SLOT_ID } from '@/components/layout/header-slot';
 import { usePathname } from 'next/navigation';
+import { resolvePageTitle, useNavStore } from '@/lib/stores/nav-store';
 
 export function Header() {
   const t = useTranslations();
@@ -95,14 +96,25 @@ export function Header() {
 
   const roleLabel = user ? tHeader(`role.${user.role}`) : '';
 
+  // Seitentitel in der Mitte (Design „Mosaik“): statt immer „Startseite“
+  // der Name der aktuellen Seite bzw. des Moduls.
+  const navModules = useNavStore((s) => s.modules);
+  const pageTitle = resolvePageTitle(pathname, navModules);
+  const pageTitleText = pageTitle
+    ? 'key' in pageTitle
+      ? t(pageTitle.key)
+      : pageTitle.text
+    : null;
+
   return (
-    <header className="sticky top-0 z-50 flex h-[var(--header-height)] items-center border-b border-border bg-background px-4 shadow-sm">
-      {/* Left: Logo + Mobile hamburger */}
-      <div className="flex shrink-0 items-center gap-3">
+    <header className="sticky top-0 z-50 flex h-[var(--header-height)] items-center bg-appbar px-2 text-appbar-foreground sm:px-3 dark:shadow-[inset_0_-1px_0_oklch(1_0_0/0.07)]">
+      {/* Links: Menue (mobil) + Bildmarke. Dunkle App-Leiste wie bei GitHub
+          bzw. Microsoft 365 — in beiden Erscheinungsbildern dunkel. */}
+      <div className="flex shrink-0 items-center gap-2">
         <button
           type="button"
           onClick={() => setMobileOpen(true)}
-          className="inline-flex items-center justify-center rounded-md p-2 text-muted-foreground hover:bg-muted hover:text-foreground transition-colors md:hidden"
+          className="inline-flex h-8 w-8 items-center justify-center rounded-md text-appbar-muted hover:bg-appbar-hover hover:text-appbar-foreground transition-colors md:hidden"
           aria-label={t('common.menu')}
         >
           <svg
@@ -122,17 +134,21 @@ export function Header() {
             <line x1="3" y1="18" x2="21" y2="18" />
           </svg>
         </button>
-        <TesseraLogo
-          variant="horizontal"
-          size={28}
-          // Gelb traegt nur auf dunklem Grund: gemessen 13,1:1 im dunklen
-          // Erscheinungsbild gegen 1,26:1 im hellen (WCAG verlangt 3:1 fuer
-          // grossen fetten Text). Im hellen Modus erbt der Schriftzug daher
-          // die Vordergrundfarbe, im dunklen steht die Markenfarbe.
-          // Unter 640 px nur die Bildmarke: der Platz gehoert dort den
-          // Dashboard-Reitern in der Kopfzeilenmitte (260924-h7x).
-          wordmarkClassName="hidden sm:inline dark:text-primary"
-        />
+        <Link
+          href="/"
+          className="flex items-center rounded-md px-1 py-1 focus-visible:outline-2 focus-visible:outline-offset-[-2px] focus-visible:outline-appbar-foreground"
+        >
+          <TesseraLogo
+            variant="horizontal"
+            size={26}
+            plateOutline="always"
+            className="gap-2.5"
+            // Schriftzug weiss auf der dunklen Leiste (in beiden
+            // Erscheinungsbildern). Unter 640 px nur die Bildmarke: der Platz
+            // gehoert dort den Dashboard-Reitern (260924-h7x).
+            wordmarkClassName="hidden sm:inline text-[15px] font-semibold tracking-normal text-appbar-foreground"
+          />
+        </Link>
       </div>
 
       {/* Mitte: Einhaengepunkt fuer die Dashboard-Reiter (quick-260924-h7x).
@@ -143,15 +159,15 @@ export function Header() {
           und Aktionen rechts auch bei schmalem Fenster Platz behalten. */}
       <div className="flex min-w-0 flex-1 items-center justify-center px-2 text-center md:px-4">
         <div id={HEADER_CENTER_SLOT_ID} className="flex min-w-0 max-w-full justify-center" />
-        {pathname !== '/' && (
-          <span className="text-sm text-muted-foreground truncate">
-            {tHeader('breadcrumb.home')}
+        {pageTitleText !== null && (
+          <span className="truncate text-sm font-semibold text-appbar-foreground">
+            {pageTitleText}
           </span>
         )}
       </div>
 
       {/* Right: Actions */}
-      <div className="flex shrink-0 items-center gap-2">
+      <div className="flex shrink-0 items-center gap-1">
         <BugReportButton />
         <ThemeToggle />
 
@@ -160,7 +176,7 @@ export function Header() {
           <button
             type="button"
             onClick={() => setDropdownOpen(!dropdownOpen)}
-            className="h-8 w-8 rounded-full overflow-hidden bg-primary flex items-center justify-center text-xs font-medium text-primary-foreground hover:opacity-90 transition-opacity"
+            className="ml-1 flex h-8 w-8 items-center justify-center overflow-hidden rounded-full bg-primary text-xs font-semibold text-primary-foreground ring-1 ring-white/15 transition-opacity hover:opacity-90 focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-appbar-foreground"
             aria-label={tHeader('userMenu')}
           >
             {user?.hasAvatar && !avatarError ? (
@@ -178,7 +194,7 @@ export function Header() {
 
           {/* Dropdown menu */}
           {dropdownOpen && (
-            <div className="absolute right-0 top-full mt-2 w-56 rounded-md border border-border bg-card shadow-lg py-2 z-50">
+            <div className="absolute right-0 top-full z-50 mt-2 w-60 rounded-lg border border-border bg-card py-1.5 text-card-foreground shadow-lg">
               {/* User info */}
               <div className="px-4 py-2 border-b border-border">
                 <p className="text-sm font-medium text-foreground truncate">
diff --git a/apps/web/src/components/layout/page-header.tsx b/apps/web/src/components/layout/page-header.tsx
new file mode 100644
index 0000000..a9816a2
--- /dev/null
+++ b/apps/web/src/components/layout/page-header.tsx
@@ -0,0 +1,32 @@
+import type { ReactNode } from 'react';
+import { ModuleTile } from '@/components/modules/module-tile';
+
+interface PageHeaderProps {
+  title: ReactNode;
+  description?: ReactNode;
+  /** Aktionen rechtsbuendig (Knoepfe, Verweise). */
+  actions?: ReactNode;
+  /** Modulkennung: zeigt die App-Kachel des Moduls links neben dem Titel. */
+  moduleSlug?: string;
+  className?: string;
+}
+
+/**
+ * Einheitlicher Seitenkopf (Design „Mosaik“, Fluent-Typografie): Titel
+ * 24/32 px halbfett, optionale Beschreibung 14 px gedaempft, Aktionen rechts.
+ * Modulseiten tragen ihre App-Kachel (36 px) links vom Titel.
+ */
+export function PageHeader({ title, description, actions, moduleSlug, className = '' }: PageHeaderProps) {
+  return (
+    <div className={`flex flex-wrap items-start justify-between gap-x-6 gap-y-3 ${className}`}>
+      <div className="flex min-w-0 items-center gap-3">
+        {moduleSlug && <ModuleTile slug={moduleSlug} size={36} />}
+        <div className="min-w-0">
+          <h1 className="text-2xl font-semibold text-foreground">{title}</h1>
+          {description && <p className="mt-0.5 text-sm text-muted-foreground">{description}</p>}
+        </div>
+      </div>
+      {actions && <div className="flex shrink-0 flex-wrap items-center gap-2">{actions}</div>}
+    </div>
+  );
+}
diff --git a/apps/web/src/components/layout/sidebar-search.tsx b/apps/web/src/components/layout/sidebar-search.tsx
index 0582e9f..c2185f6 100644
--- a/apps/web/src/components/layout/sidebar-search.tsx
+++ b/apps/web/src/components/layout/sidebar-search.tsx
@@ -11,14 +11,32 @@ export function SidebarSearch({ value, onChange }: SidebarSearchProps) {
   const t = useTranslations('sidebar');
 
   return (
-    <div className="px-3 pb-2">
+    <div className="relative pb-2">
+      <svg
+        aria-hidden="true"
+        xmlns="http://www.w3.org/2000/svg"
+        width="16"
+        height="16"
+        viewBox="0 0 24 24"
+        fill="none"
+        stroke="currentColor"
+        strokeWidth="2"
+        strokeLinecap="round"
+        strokeLinejoin="round"
+        className="pointer-events-none absolute left-2.5 top-2 text-muted-foreground"
+      >
+        <circle cx="11" cy="11" r="7" />
+        <path d="m20 20-3.5-3.5" />
+      </svg>
+      {/* Gefuelltes Suchfeld ohne harten Rahmen (Fluent „filled“); Fokus =
+          2 px Akzentlinie unten plus Tastaturring. */}
       <input
-        type="text"
+        type="search"
         value={value}
         onChange={(e) => onChange(e.target.value)}
         placeholder={t('search')}
         aria-label={t('search')}
-        className="flex h-9 w-full rounded-md border border-border bg-background px-3 text-sm ring-offset-background focus:outline-none focus:ring-2 focus:ring-ring focus:border-transparent"
+        className="flex h-8 w-full rounded-md border-0 bg-sidebar-hover pl-8 pr-2.5 text-sm text-foreground placeholder:text-muted-foreground shadow-[inset_0_-1px_0_var(--input)] transition-shadow focus:bg-card focus:shadow-[inset_0_-2px_0_var(--primary-strong)] focus:outline-none [&::-webkit-search-cancel-button]:hidden"
       />
     </div>
   );
diff --git a/apps/web/src/components/layout/sidebar.test.tsx b/apps/web/src/components/layout/sidebar.test.tsx
index 4f78d17..87d47bc 100644
--- a/apps/web/src/components/layout/sidebar.test.tsx
+++ b/apps/web/src/components/layout/sidebar.test.tsx
@@ -147,12 +147,10 @@ describe('Sidebar', () => {
     const Sidebar = await importSidebar();
     render(<Sidebar />);
 
-    // Categories are collapsed by default — wait for category header, then expand
+    // Design „Mosaik“: Kategorien sind anfangs aufgeklappt.
     await waitFor(() => {
-      expect(screen.getByText('Domain Tools')).toBeInTheDocument();
+      expect(screen.getByText('Domain-Tools')).toBeInTheDocument();
     });
-    await userEvent.click(screen.getByText('Domain Tools'));
-
     await waitFor(() => {
       expect(screen.getByText('Domaincheck')).toBeInTheDocument();
     });
@@ -165,13 +163,46 @@ describe('Sidebar', () => {
     });
   });
 
+  it('Kategorien sind aufgeklappt, ein Klick auf die Kopfzeile klappt zu und wieder auf', async () => {
+    const Sidebar = await importSidebar();
+    render(<Sidebar />);
+
+    await waitFor(() => {
+      expect(screen.getByText('Domaincheck')).toBeInTheDocument();
+    });
+    const header = screen.getByText('Domain-Tools').closest('button');
+    expect(header).toHaveAttribute('aria-expanded', 'true');
+
+    await userEvent.click(screen.getByText('Domain-Tools'));
+    expect(screen.queryByText('Domaincheck')).not.toBeInTheDocument();
+    expect(header).toHaveAttribute('aria-expanded', 'false');
+
+    await userEvent.click(screen.getByText('Domain-Tools'));
+    expect(screen.getByText('Domaincheck')).toBeInTheDocument();
+  });
+
+  it('Modul-Eintraege tragen die App-Kachel, die Auswahl die Akzent-Pille', async () => {
+    mockPathname = '/modules/Domain-Tools/domaincheck';
+    const Sidebar = await importSidebar();
+    render(<Sidebar />);
+
+    await waitFor(() => {
+      expect(screen.getByText('Domaincheck')).toBeInTheDocument();
+    });
+    const link = screen.getByText('Domaincheck').closest('a');
+    expect(link?.querySelector('[data-module-tile="domaincheck"]')).not.toBeNull();
+    expect(link?.querySelector('[data-testid="nav-selection-pill"]')).not.toBeNull();
+    const dashLink = screen.getByText('Dashboard').closest('a');
+    expect(dashLink?.querySelector('[data-testid="nav-selection-pill"]')).toBeNull();
+  });
+
   it('re-fetches modules when sidebarRefreshKey changes', async () => {
     const Sidebar = await importSidebar();
     const { rerender } = render(<Sidebar />);
 
     // Wait for category header to confirm initial fetch completed
     await waitFor(() => {
-      expect(screen.getByText('Domain Tools')).toBeInTheDocument();
+      expect(screen.getByText('Domain-Tools')).toBeInTheDocument();
     });
 
     const initialCallCount = (globalThis.fetch as ReturnType<typeof vi.fn>).mock.calls.length;
diff --git a/apps/web/src/components/layout/sidebar.tsx b/apps/web/src/components/layout/sidebar.tsx
index 6940364..298035e 100644
--- a/apps/web/src/components/layout/sidebar.tsx
+++ b/apps/web/src/components/layout/sidebar.tsx
@@ -9,6 +9,20 @@ import { useSidebarStore } from '@/lib/stores/sidebar-store';
 import { useMarketplaceStore } from '@/lib/stores/marketplace-store';
 import { SidebarSearch } from '@/components/layout/sidebar-search';
 import { AppVersionBadge } from '@/components/layout/app-version-badge';
+import { ModuleTile } from '@/components/modules/module-tile';
+import { useCategoryLabel } from '@/lib/use-category-label';
+import { useNavStore } from '@/lib/stores/nav-store';
+
+/** Fluent-Auswahlmarke: 3 x 16 px Pille am linken Rand des gewaehlten Eintrags. */
+function SelectionPill() {
+  return (
+    <span
+      aria-hidden="true"
+      data-testid="nav-selection-pill"
+      className="absolute left-0 top-1/2 h-4 w-[3px] -translate-y-1/2 rounded-full bg-primary-strong"
+    />
+  );
+}
 
 const API_URL = process.env.NEXT_PUBLIC_API_URL || 'http://localhost:3001';
 
@@ -25,7 +39,11 @@ export function Sidebar() {
   const { isCollapsed, isMobileOpen, toggle, setMobileOpen } = useSidebarStore();
   const [activeModules, setActiveModules] = useState<SidebarModule[]>([]);
   const [searchQuery, setSearchQuery] = useState('');
-  const [openCategories, setOpenCategories] = useState<Set<string>>(new Set());
+  // Kategorien sind anfangs aufgeklappt (Design „Mosaik“): die Modul-Kacheln
+  // sind der wichtigste Wegweiser. Gemerkt werden die ZUGEKLAPPTEN.
+  const [closedCategories, setClosedCategories] = useState<Set<string>>(new Set());
+  const categoryLabel = useCategoryLabel();
+  const setNavModules = useNavStore((s) => s.setModules);
   const pathname = usePathname();
   const sidebarRefreshKey = useMarketplaceStore((s) => s.sidebarRefreshKey);
 
@@ -34,25 +52,34 @@ export function Sidebar() {
     return pathname.startsWith(href);
   };
 
-  const linkClass = (href: string) =>
-    `flex items-center gap-3 rounded-md px-2 py-2 text-sm transition-colors ${
-      isActive(href)
-        ? 'bg-sidebar-accent text-sidebar-accent-foreground font-medium'
-        : 'text-sidebar-foreground hover:bg-muted'
+  // Design „Mosaik“ (Fluent 2): 36 px hohe Eintraege, 8 px Radius, die
+  // Auswahl traegt eine neutrale Flaeche, halbfette Schrift und links eine
+  // 3 x 16 px grosse Pille in der Akzentfarbe (`SelectionPill`).
+  const itemClass = (active: boolean) =>
+    `relative flex h-9 items-center gap-3 rounded-lg text-sm transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-inset focus-visible:ring-ring ${
+      isCollapsed ? 'justify-center px-0' : 'px-2.5'
+    } ${
+      active
+        ? 'bg-sidebar-accent font-semibold text-sidebar-accent-foreground'
+        : 'text-sidebar-foreground hover:bg-sidebar-hover'
     }`;
 
+  const linkClass = (href: string) => itemClass(isActive(href));
+
   const fetchActiveModules = useCallback(async () => {
     try {
       const res = await fetch(`${API_URL}/modules/active`, {
         credentials: 'include',
       });
       if (res.ok) {
-        setActiveModules(await res.json());
+        const modules: SidebarModule[] = await res.json();
+        setActiveModules(modules);
+        setNavModules(modules);
       }
     } catch {
       // silently fail
     }
-  }, []);
+  }, [setNavModules]);
 
   // Befund 17 (quick-260921-gof): sidebarRefreshKey ist der Auffrisch-
   // Ausloeser aus dem Marketplace-Speicher — ohne ihn erscheint ein frisch
@@ -64,7 +91,7 @@ export function Sidebar() {
   }, [fetchActiveModules, sidebarRefreshKey]);
 
   const toggleCategory = (cat: string) => {
-    setOpenCategories((prev) => {
+    setClosedCategories((prev) => {
       const next = new Set(prev);
       if (next.has(cat)) next.delete(cat);
       else next.add(cat);
@@ -85,7 +112,7 @@ export function Sidebar() {
     const q = searchQuery.toLowerCase();
     const result: [string, SidebarModule[]][] = [];
     for (const [cat, mods] of categories.entries()) {
-      if (cat.toLowerCase().includes(q)) {
+      if (cat.toLowerCase().includes(q) || categoryLabel(cat).toLowerCase().includes(q)) {
         result.push([cat, mods]);
       } else {
         const filtered = mods.filter((m) => m.name.toLowerCase().includes(q));
@@ -93,115 +120,136 @@ export function Sidebar() {
       }
     }
     return result;
-  }, [activeModules, searchQuery]);
+  }, [activeModules, searchQuery, categoryLabel]);
+
+  const navIcon = (children: React.ReactNode) => (
+    <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="1.75" strokeLinecap="round" strokeLinejoin="round" className="shrink-0">
+      {children}
+    </svg>
+  );
 
   const sidebarContent = (
     <div className="flex h-full flex-col bg-sidebar">
-      <nav className="flex-1 overflow-y-auto p-3">
-        <ul className="flex flex-col gap-1">
+      <nav className={`flex-1 overflow-y-auto py-3 ${isCollapsed ? 'px-2' : 'px-3'}`}>
+        <ul className="flex flex-col gap-0.5">
           <li>
-            <Link href="/" className={linkClass('/')} aria-label={t('dashboard')}>
-              <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" className="shrink-0">
-                <rect x="3" y="3" width="7" height="7" />
-                <rect x="14" y="3" width="7" height="7" />
-                <rect x="14" y="14" width="7" height="7" />
-                <rect x="3" y="14" width="7" height="7" />
-              </svg>
+            <Link href="/" className={linkClass('/')} aria-label={t('dashboard')} title={isCollapsed ? t('dashboard') : undefined}>
+              {isActive('/') && <SelectionPill />}
+              {navIcon(
+                <>
+                  <rect x="3" y="3" width="7" height="9" rx="1.5" />
+                  <rect x="14" y="3" width="7" height="5" rx="1.5" />
+                  <rect x="14" y="12" width="7" height="9" rx="1.5" />
+                  <rect x="3" y="16" width="7" height="5" rx="1.5" />
+                </>,
+              )}
               {!isCollapsed && <span className="truncate">{t('dashboard')}</span>}
             </Link>
           </li>
           <li>
-            <Link href="/marketplace" className={linkClass('/marketplace')} aria-label={t('marketplace')}>
-              <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" className="shrink-0">
-                <circle cx="9" cy="21" r="1" />
-                <circle cx="20" cy="21" r="1" />
-                <path d="M1 1h4l2.68 13.39a2 2 0 0 0 2 1.61h9.72a2 2 0 0 0 2-1.61L23 6H6" />
-              </svg>
+            <Link href="/marketplace" className={linkClass('/marketplace')} aria-label={t('marketplace')} title={isCollapsed ? t('marketplace') : undefined}>
+              {isActive('/marketplace') && <SelectionPill />}
+              {navIcon(
+                <>
+                  <path d="M3 9h18l-1.5 10.5a2 2 0 0 1-2 1.5h-11a2 2 0 0 1-2-1.5z" />
+                  <path d="M8 9V7a4 4 0 0 1 8 0v2" />
+                </>,
+              )}
               {!isCollapsed && <span className="truncate">{t('marketplace')}</span>}
             </Link>
           </li>
         </ul>
 
+        {/* Eingeklappt: nur die Modul-Kacheln untereinander (Name als Tooltip). */}
+        {isCollapsed && activeModules.length > 0 && (
+          <ul className="mt-3 flex flex-col gap-0.5 border-t border-sidebar-border pt-3">
+            {activeModules.map((mod) => {
+              const href = `/modules/${mod.category || 'other'}/${mod.slug}`;
+              const active = isActive(href) || isActive(`/modules/${mod.slug}`);
+              return (
+                <li key={mod.id}>
+                  <Link href={href} className={itemClass(active)} aria-label={mod.name} title={mod.name}>
+                    {active && <SelectionPill />}
+                    <ModuleTile slug={mod.slug} size={20} />
+                  </Link>
+                </li>
+              );
+            })}
+          </ul>
+        )}
+
         {!isCollapsed && (
           <>
-            <div className="mt-4">
+            <div className="mt-4 border-t border-sidebar-border pt-3">
               <SidebarSearch value={searchQuery} onChange={setSearchQuery} />
             </div>
 
-            <div className="mt-2">
-              <div className="px-2 py-2 text-xs font-semibold uppercase tracking-wider text-muted-foreground">
-                {t('categories.label')}
-              </div>
-              <div className="mt-1">
-                {activeModules.length === 0 ? (
-                  <div className="px-2 py-2 text-sm text-muted-foreground">
-                    {t('categories.empty')}
-                  </div>
-                ) : filteredCategories.length === 0 ? (
-                  <div className="px-2 py-2 text-sm text-muted-foreground">
-                    {t('noResults')}
-                  </div>
-                ) : (
-                  <ul className="flex flex-col gap-1">
-                    {filteredCategories.map(([category, mods]) => (
+            <div className="mt-1" aria-label={t('categories.label')} role="group">
+              {activeModules.length === 0 ? (
+                <div className="px-2.5 py-2 text-sm text-muted-foreground">
+                  {t('categories.empty')}
+                </div>
+              ) : filteredCategories.length === 0 ? (
+                <div className="px-2.5 py-2 text-sm text-muted-foreground">
+                  {t('noResults')}
+                </div>
+              ) : (
+                <ul className="flex flex-col gap-2">
+                  {filteredCategories.map(([category, mods]) => {
+                    // Bei aktiver Suche immer aufgeklappt, sonst nach Wahl.
+                    const open = searchQuery !== '' || !closedCategories.has(category);
+                    return (
                       <li key={category}>
                         <button
                           type="button"
                           onClick={() => toggleCategory(category)}
-                          className={`flex w-full items-center gap-2 rounded-md px-2 py-1.5 text-xs font-medium transition-colors ${
-                            isActive(`/modules/${category}`)
-                              ? 'bg-sidebar-accent text-sidebar-accent-foreground'
-                              : 'text-muted-foreground hover:bg-muted hover:text-foreground'
-                          }`}
+                          aria-expanded={open}
+                          className="group flex h-7 w-full items-center gap-1.5 rounded-md px-2.5 text-xs font-semibold text-muted-foreground transition-colors hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-inset focus-visible:ring-ring"
                         >
-                          <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" className="shrink-0">
-                            <path d="M22 19a2 2 0 0 1-2 2H4a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h5l2 3h9a2 2 0 0 1 2 2z" />
+                          <span className="truncate">{categoryLabel(category)}</span>
+                          <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.25" strokeLinecap="round" strokeLinejoin="round" className={`ml-auto shrink-0 opacity-70 transition-transform duration-150 ${open ? '' : '-rotate-90'}`}>
+                            <polyline points="6 9 12 15 18 9" />
                           </svg>
-                          <span className="capitalize">{category.replace(/-/g, ' ')}</span>
-                          <span className="ml-auto flex items-center gap-1.5">
-                            <span className="text-[10px] text-muted-foreground/60">{mods.length}</span>
-                            <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" className={`transition-transform duration-200 ${openCategories.has(category) ? 'rotate-180' : ''}`}>
-                              <polyline points="6 9 12 15 18 9" />
-                            </svg>
-                          </span>
                         </button>
-                        {openCategories.has(category) && (
-                          <ul className="ml-5 flex flex-col gap-0.5">
-                            {mods.map((mod) => (
-                              <li key={mod.id}>
-                                <Link
-                                  href={`/modules/${category}/${mod.slug}`}
-                                  className={`block rounded-md px-2 py-1 text-xs transition-colors ${
-                                    isActive(`/modules/${category}/${mod.slug}`)
-                                      ? 'bg-sidebar-accent text-sidebar-accent-foreground font-medium'
-                                      : 'text-muted-foreground hover:bg-muted hover:text-foreground'
-                                  }`}
-                                >
-                                  {mod.name}
-                                </Link>
-                              </li>
-                            ))}
+                        {open && (
+                          <ul className="mt-0.5 flex flex-col gap-0.5">
+                            {mods.map((mod) => {
+                              const href = `/modules/${category}/${mod.slug}`;
+                              const active = isActive(href) || isActive(`/modules/${mod.slug}`);
+                              return (
+                                <li key={mod.id}>
+                                  <Link href={href} className={itemClass(active)}>
+                                    {active && <SelectionPill />}
+                                    <ModuleTile slug={mod.slug} size={20} />
+                                    <span className="truncate">{mod.name}</span>
+                                  </Link>
+                                </li>
+                              );
+                            })}
                           </ul>
                         )}
                       </li>
-                    ))}
-                  </ul>
-                )}
-              </div>
+                    );
+                  })}
+                </ul>
+              )}
             </div>
           </>
         )}
       </nav>
 
-      <div className="hidden md:block border-t border-sidebar-border p-2">
+      <div className="hidden border-t border-sidebar-border px-3 py-2 md:block">
         <button
           type="button"
           onClick={toggle}
-          className="flex w-full items-center gap-3 rounded-md px-2 py-1.5 text-sm text-sidebar-foreground hover:bg-muted transition-colors"
+          className={`flex h-8 w-full items-center gap-3 rounded-lg text-sm text-muted-foreground transition-colors hover:bg-sidebar-hover hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-inset focus-visible:ring-ring ${isCollapsed ? 'justify-center' : 'px-2.5'}`}
           aria-label={isCollapsed ? t('expand') : t('collapse')}
+          title={isCollapsed ? t('expand') : undefined}
         >
-          <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" className={`shrink-0 transition-transform duration-200 ${isCollapsed ? 'rotate-180' : ''}`}>
-            <polyline points="15 18 9 12 15 6" />
+          <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="1.75" strokeLinecap="round" strokeLinejoin="round" className={`shrink-0 transition-transform duration-200 ${isCollapsed ? 'rotate-180' : ''}`}>
+            <rect x="3" y="3" width="18" height="18" rx="2" />
+            <path d="M9 3v18" />
+            <path d="m16 15-3-3 3-3" />
           </svg>
           {!isCollapsed && <span className="truncate">{t('collapse')}</span>}
         </button>
@@ -210,7 +258,7 @@ export function Sidebar() {
       {/* Versionszeile (quick-260914-ku1): bewusst ohne `hidden md:block`, damit
           auch die mobile Schublade sie zeigt; eingeklappt nichts (Muster oben). */}
       {!isCollapsed && (
-        <div className="border-t border-sidebar-border px-4 py-2">
+        <div className="px-5 pb-3 pt-1">
           <AppVersionBadge />
         </div>
       )}
@@ -220,7 +268,7 @@ export function Sidebar() {
   return (
     <>
       <aside
-        className="fixed left-0 top-[var(--header-height)] z-30 hidden h-[calc(100vh-var(--header-height))] border-r border-sidebar-border transition-all duration-200 md:block"
+        className="fixed left-0 top-[var(--header-height)] z-30 hidden h-[calc(100vh-var(--header-height))] border-r border-sidebar-border transition-[width] duration-200 md:block"
         style={{
           width: isCollapsed
             ? 'var(--sidebar-width-collapsed)'
@@ -237,22 +285,21 @@ export function Sidebar() {
             onClick={() => setMobileOpen(false)}
             aria-hidden="true"
           />
-          <aside className="fixed left-0 top-0 z-50 h-full w-[var(--sidebar-width)] bg-sidebar shadow-lg">
-            <div className="flex h-[var(--header-height)] items-center justify-between border-b border-sidebar-border px-4">
+          <aside className="fixed left-0 top-0 z-50 flex h-full w-[var(--sidebar-width)] flex-col bg-sidebar shadow-xl">
+            {/* Kopf der Schublade im Stil der App-Leiste (immer dunkel). */}
+            <div className="flex h-[var(--header-height)] items-center justify-between bg-appbar px-3 text-appbar-foreground">
               <TesseraLogo
-                      variant="horizontal"
-                      size={28}
-                      // Gelb traegt nur auf dunklem Grund: gemessen 13,1:1 im dunklen
-                      // Erscheinungsbild gegen 1,26:1 im hellen (WCAG verlangt 3:1 fuer
-                      // grossen fetten Text). Im hellen Modus erbt der Schriftzug daher
-                      // die Vordergrundfarbe, im dunklen steht die Markenfarbe.
-                      wordmarkClassName="dark:text-primary"
-                    />
+                variant="horizontal"
+                size={26}
+                plateOutline="always"
+                className="gap-2.5"
+                wordmarkClassName="text-[15px] font-semibold tracking-normal text-appbar-foreground"
+              />
               <button
                 type="button"
                 onClick={() => setMobileOpen(false)}
                 aria-label={tCommon('close')}
-                className="rounded-md p-2 text-muted-foreground hover:bg-muted hover:text-foreground transition-colors"
+                className="inline-flex h-8 w-8 items-center justify-center rounded-md text-appbar-muted transition-colors hover:bg-appbar-hover hover:text-appbar-foreground"
               >
                 <svg aria-hidden="true" xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
                   <line x1="18" y1="6" x2="6" y2="18" />
@@ -260,7 +307,7 @@ export function Sidebar() {
                 </svg>
               </button>
             </div>
-            {sidebarContent}
+            <div className="min-h-0 flex-1">{sidebarContent}</div>
           </aside>
         </div>
       )}
diff --git a/apps/web/src/components/theme-toggle.tsx b/apps/web/src/components/theme-toggle.tsx
index b929aba..85ea641 100644
--- a/apps/web/src/components/theme-toggle.tsx
+++ b/apps/web/src/components/theme-toggle.tsx
@@ -35,7 +35,7 @@ export function ThemeToggle() {
     <button
       type="button"
       onClick={cycleTheme}
-      className="inline-flex items-center justify-center rounded-md p-2 text-muted-foreground hover:bg-muted hover:text-foreground transition-colors"
+      className="inline-flex h-8 w-8 items-center justify-center rounded-md text-appbar-muted hover:bg-appbar-hover hover:text-appbar-foreground transition-colors focus-visible:outline-2 focus-visible:outline-offset-[-2px] focus-visible:outline-appbar-foreground"
       aria-label={label}
       title={label}
     >
diff --git a/apps/web/src/lib/stores/nav-store.ts b/apps/web/src/lib/stores/nav-store.ts
new file mode 100644
index 0000000..e8c44c7
--- /dev/null
+++ b/apps/web/src/lib/stores/nav-store.ts
@@ -0,0 +1,62 @@
+import { create } from 'zustand';
+
+export interface NavModule {
+  id: string;
+  slug: string;
+  name: string;
+  category: string;
+}
+
+interface NavState {
+  /** Freigegebene Module, wie die Seitenleiste sie geladen hat. */
+  modules: NavModule[];
+  setModules: (modules: NavModule[]) => void;
+}
+
+/**
+ * Geteilter Stand der Seitenleiste: die Kopfzeile liest daraus den
+ * Modulnamen fuer den Seitentitel, ohne selbst noch einmal zu laden.
+ */
+export const useNavStore = create<NavState>()((set) => ({
+  modules: [],
+  setModules: (modules) => set({ modules }),
+}));
+
+/** Ersatztitel, solange die Seitenleiste die Module noch nicht geladen hat. */
+const MODULE_TITLE_KEYS: Record<string, string> = {
+  proxmox: 'proxmox.title',
+  domaincheck: 'domaincheck.title',
+  'cert-manager': 'certManager.title',
+  'dkv-fleet': 'dkvFleet.pageTitle',
+  'tender-radar': 'tenderRadar.page.title',
+};
+
+/**
+ * Seitentitel der Kopfzeile zu einem Pfad. `null` auf der Startseite (dort
+ * stehen die Dashboard-Reiter), sonst ein Uebersetzungsschluessel oder ein
+ * fertiger Modulname.
+ */
+export function resolvePageTitle(
+  pathname: string,
+  modules: NavModule[],
+): { key: string } | { text: string } | null {
+  if (pathname === '/') return null;
+  if (pathname.startsWith('/marketplace')) return { key: 'sidebar.marketplace' };
+  if (pathname.startsWith('/settings')) return { key: 'sidebar.settings' };
+  if (pathname.startsWith('/changelog')) return { key: 'sidebar.whatsNew' };
+  if (pathname.startsWith('/admin')) return { key: 'sidebar.admin' };
+  if (pathname.startsWith('/change-password')) return { key: 'auth.changePassword.title' };
+  if (pathname.startsWith('/modules/')) {
+    const segments = pathname.split('/').filter(Boolean).slice(1);
+    for (const segment of segments) {
+      const mod = modules.find((m) => m.slug === segment);
+      if (mod) return { text: mod.name };
+    }
+    for (const segment of segments) {
+      const key = MODULE_TITLE_KEYS[segment];
+      if (key) return { key };
+    }
+    return { text: '' };
+  }
+  return { key: 'header.breadcrumb.home' };
+}