feat(01-02): design token system, i18n framework, and theme provider setup

- OKLCH design tokens with yellow #ffed00 primary and dark gray-blue dark mode
- next-intl cookie-based locale with DE/EN message files
- next-themes provider with system/light/dark support
- Sidebar and header layout dimension tokens
- Root layout with ThemeProvider and NextIntlClientProvider wrappers

apps/web/src/app/globals.css

@@ -1 +1,98 @@
 @import "tailwindcss";
+
+@theme inline {
+  --color-primary: var(--primary);
+  --color-primary-foreground: var(--primary-foreground);
+  --color-secondary: var(--secondary);
+  --color-secondary-foreground: var(--secondary-foreground);
+  --color-accent: var(--accent);
+  --color-accent-foreground: var(--accent-foreground);
+  --color-background: var(--background);
+  --color-foreground: var(--foreground);
+  --color-card: var(--card);
+  --color-card-foreground: var(--card-foreground);
+  --color-muted: var(--muted);
+  --color-muted-foreground: var(--muted-foreground);
+  --color-destructive: var(--destructive);
+  --color-destructive-foreground: var(--destructive-foreground);
+  --color-border: var(--border);
+  --color-input: var(--input);
+  --color-ring: var(--ring);
+  --color-sidebar: var(--sidebar);
+  --color-sidebar-foreground: var(--sidebar-foreground);
+  --color-sidebar-accent: var(--sidebar-accent);
+  --color-sidebar-accent-foreground: var(--sidebar-accent-foreground);
+  --color-sidebar-border: var(--sidebar-border);
+  --radius-sm: calc(var(--radius) - 2px);
+  --radius-md: var(--radius);
+  --radius-lg: calc(var(--radius) + 2px);
+}
+
+:root {
+  --radius: 0.5rem;
+  --font-sans: "Inter", system-ui, -apple-system, sans-serif;
+
+  /* Layout dimensions */
+  --sidebar-width: 240px;
+  --sidebar-width-collapsed: 64px;
+  --header-height: 60px;
+
+  /* Light mode colors (OKLCH) */
+  --background: oklch(0.99 0 0);
+  --foreground: oklch(0.15 0 0);
+  --card: oklch(1 0 0);
+  --card-foreground: oklch(0.15 0 0);
+  --primary: oklch(0.91 0.19 102);
+  --primary-foreground: oklch(0.20 0.02 90);
+  --secondary: oklch(0.96 0 0);
+  --secondary-foreground: oklch(0.15 0 0);
+  --muted: oklch(0.96 0 0);
+  --muted-foreground: oklch(0.55 0 0);
+  --accent: oklch(0.96 0 0);
+  --accent-foreground: oklch(0.15 0 0);
+  --destructive: oklch(0.55 0.2 27);
+  --destructive-foreground: oklch(0.98 0 0);
+  --border: oklch(0.90 0 0);
+  --input: oklch(0.90 0 0);
+  --ring: oklch(0.91 0.19 102);
+
+  /* Sidebar tokens */
+  --sidebar: oklch(0.97 0 0);
+  --sidebar-foreground: oklch(0.15 0 0);
+  --sidebar-accent: oklch(0.91 0.19 102 / 0.1);
+  --sidebar-accent-foreground: oklch(0.91 0.19 102);
+  --sidebar-border: oklch(0.90 0 0);
+}
+
+.dark {
+  --background: oklch(0.17 0.01 260);
+  --foreground: oklch(0.95 0 0);
+  --card: oklch(0.21 0.01 260);
+  --card-foreground: oklch(0.95 0 0);
+  --primary: oklch(0.91 0.19 102);
+  --primary-foreground: oklch(0.20 0.02 90);
+  --secondary: oklch(0.25 0.01 260);
+  --secondary-foreground: oklch(0.95 0 0);
+  --muted: oklch(0.25 0.01 260);
+  --muted-foreground: oklch(0.65 0 0);
+  --accent: oklch(0.25 0.01 260);
+  --accent-foreground: oklch(0.95 0 0);
+  --destructive: oklch(0.55 0.2 27);
+  --destructive-foreground: oklch(0.98 0 0);
+  --border: oklch(0.30 0.01 260);
+  --input: oklch(0.30 0.01 260);
+  --ring: oklch(0.91 0.19 102);
+
+  /* Sidebar tokens (dark) */
+  --sidebar: oklch(0.14 0.01 260);
+  --sidebar-foreground: oklch(0.95 0 0);
+  --sidebar-accent: oklch(0.91 0.19 102 / 0.15);
+  --sidebar-accent-foreground: oklch(0.91 0.19 102);
+  --sidebar-border: oklch(0.30 0.01 260);
+}
+
+body {
+  font-family: var(--font-sans);
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}

apps/web/src/app/layout.tsx

@@ -1,4 +1,7 @@
 import type { Metadata } from 'next';
+import { NextIntlClientProvider } from 'next-intl';
+import { getLocale, getMessages } from 'next-intl/server';
+import { ThemeProvider } from 'next-themes';
 import './globals.css';
 
 export const metadata: Metadata = {
@@ -6,15 +9,27 @@ export const metadata: Metadata = {
   description: 'Modulare Workflow-Plattform',
 };
 
-export default function RootLayout({
+export default async function RootLayout({
   children,
 }: {
   children: React.ReactNode;
 }) {
+  const locale = await getLocale();
+  const messages = await getMessages();
+
   return (
-    <html lang="de">
-      <body className="antialiased">
-        {children}
+    <html lang={locale} suppressHydrationWarning>
+      <body className="font-sans antialiased bg-background text-foreground">
+        <ThemeProvider
+          attribute="class"
+          defaultTheme="system"
+          enableSystem
+          disableTransitionOnChange
+        >
+          <NextIntlClientProvider messages={messages}>
+            {children}
+          </NextIntlClientProvider>
+        </ThemeProvider>
       </body>
     </html>
   );

apps/web/src/i18n/request.ts

@@ -0,0 +1,12 @@
+import { getRequestConfig } from 'next-intl/server';
+import { cookies } from 'next/headers';
+
+export default getRequestConfig(async () => {
+  const cookieStore = await cookies();
+  const locale = cookieStore.get('NEXT_LOCALE')?.value || 'de';
+
+  return {
+    locale,
+    messages: (await import(`../messages/${locale}.json`)).default,
+  };
+});

apps/web/src/messages/de.json

@@ -0,0 +1,40 @@
+{
+  "common": {
+    "appName": "Tessera",
+    "loading": "Laden...",
+    "save": "Speichern",
+    "cancel": "Abbrechen"
+  },
+  "header": {
+    "search": "Suchen...",
+    "userMenu": "Benutzermenu",
+    "breadcrumb": {
+      "home": "Startseite"
+    }
+  },
+  "sidebar": {
+    "dashboard": "Dashboard",
+    "marketplace": "Marktplatz",
+    "settings": "Einstellungen",
+    "collapse": "Einklappen",
+    "expand": "Ausklappen",
+    "categories": {
+      "label": "Kategorien",
+      "empty": "Keine Module"
+    }
+  },
+  "dashboard": {
+    "title": "Dashboard",
+    "empty": "Keine Widgets aktiv",
+    "addWidget": "Widget hinzufuegen"
+  },
+  "theme": {
+    "light": "Hell",
+    "dark": "Dunkel",
+    "system": "System"
+  },
+  "locale": {
+    "de": "Deutsch",
+    "en": "English"
+  }
+}

apps/web/src/messages/en.json

@@ -0,0 +1,40 @@
+{
+  "common": {
+    "appName": "Tessera",
+    "loading": "Loading...",
+    "save": "Save",
+    "cancel": "Cancel"
+  },
+  "header": {
+    "search": "Search...",
+    "userMenu": "User menu",
+    "breadcrumb": {
+      "home": "Home"
+    }
+  },
+  "sidebar": {
+    "dashboard": "Dashboard",
+    "marketplace": "Marketplace",
+    "settings": "Settings",
+    "collapse": "Collapse",
+    "expand": "Expand",
+    "categories": {
+      "label": "Categories",
+      "empty": "No modules"
+    }
+  },
+  "dashboard": {
+    "title": "Dashboard",
+    "empty": "No active widgets",
+    "addWidget": "Add widget"
+  },
+  "theme": {
+    "light": "Light",
+    "dark": "Dark",
+    "system": "System"
+  },
+  "locale": {
+    "de": "Deutsch",
+    "en": "English"
+  }
+}