feat(02-02): login page UI, header/sidebar auth wiring, i18n keys

- Create split-screen login page with branding left (#ffed00) and form right (D-01)
- Login form has username, password, and remember-me checkbox (D-02)
- Wire header user avatar with auth store: shows user initial, dropdown with role badge and logout
- Wire sidebar footer with auth store: shows user name, role, and initial
- Add auth, header role, and admin i18n keys to both de.json and en.json
- All new UI strings use t() function (no hardcoded text)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/messages/de.json

@@ -4,13 +4,44 @@
     "loading": "Laden...",
     "save": "Speichern",
     "cancel": "Abbrechen",
-    "menu": "Menu"
+    "menu": "Menu",
+    "confirm": "Bestaetigen",
+    "delete": "Loeschen",
+    "edit": "Bearbeiten",
+    "create": "Erstellen",
+    "close": "Schliessen",
+    "yes": "Ja",
+    "no": "Nein",
+    "active": "Aktiv",
+    "inactive": "Inaktiv",
+    "actions": "Aktionen",
+    "accessDenied": "Zugriff verweigert"
+  },
+  "auth": {
+    "login": "Anmelden",
+    "username": "Benutzername",
+    "password": "Passwort",
+    "rememberMe": "Angemeldet bleiben",
+    "submit": "Anmelden",
+    "error": {
+      "invalidCredentials": "Benutzername oder Passwort ungueltig",
+      "networkError": "Verbindungsfehler. Bitte versuchen Sie es erneut."
+    },
+    "branding": {
+      "tagline": "Modulare Workflow-Plattform fuer Ihr Unternehmen"
+    }
   },
   "header": {
     "search": "Suchen...",
     "userMenu": "Benutzermenu",
     "breadcrumb": {
       "home": "Startseite"
+    },
+    "logout": "Abmelden",
+    "role": {
+      "SUPER_ADMIN": "Super-Admin",
+      "ADMIN": "Admin",
+      "USER": "Benutzer"
     }
   },
   "sidebar": {
@@ -23,13 +54,47 @@
     "categories": {
       "label": "Kategorien",
       "empty": "Keine Module"
-    }
+    },
+    "admin": "Verwaltung",
+    "users": "Benutzer",
+    "tenants": "Mandanten"
   },
   "dashboard": {
     "title": "Dashboard",
     "empty": "Keine Widgets aktiv",
     "addWidget": "Widget hinzufuegen"
   },
+  "admin": {
+    "users": {
+      "title": "Benutzerverwaltung",
+      "create": "Benutzer erstellen",
+      "edit": "Benutzer bearbeiten",
+      "delete": "Benutzer loeschen",
+      "deleteConfirm": "Moechten Sie diesen Benutzer wirklich loeschen?",
+      "name": "Name",
+      "username": "Benutzername",
+      "email": "E-Mail",
+      "displayName": "Anzeigename",
+      "role": "Rolle",
+      "status": "Status",
+      "actions": "Aktionen",
+      "password": "Passwort",
+      "noUsers": "Keine Benutzer gefunden"
+    },
+    "tenants": {
+      "title": "Mandantenverwaltung",
+      "create": "Mandant erstellen",
+      "edit": "Mandant bearbeiten",
+      "name": "Name",
+      "slug": "Slug",
+      "status": "Status",
+      "userCount": "Benutzer",
+      "actions": "Aktionen",
+      "noTenants": "Keine Mandanten gefunden",
+      "deleteConfirm": "Moechten Sie diesen Mandanten wirklich loeschen?",
+      "cannotDeleteActive": "Mandanten mit aktiven Benutzern koennen nicht geloescht werden"
+    }
+  },
   "theme": {
     "light": "Hell",
     "dark": "Dunkel",

apps/web/src/messages/en.json

@@ -4,13 +4,44 @@
     "loading": "Loading...",
     "save": "Save",
     "cancel": "Cancel",
-    "menu": "Menu"
+    "menu": "Menu",
+    "confirm": "Confirm",
+    "delete": "Delete",
+    "edit": "Edit",
+    "create": "Create",
+    "close": "Close",
+    "yes": "Yes",
+    "no": "No",
+    "active": "Active",
+    "inactive": "Inactive",
+    "actions": "Actions",
+    "accessDenied": "Access denied"
+  },
+  "auth": {
+    "login": "Sign In",
+    "username": "Username",
+    "password": "Password",
+    "rememberMe": "Remember me",
+    "submit": "Sign In",
+    "error": {
+      "invalidCredentials": "Invalid username or password",
+      "networkError": "Connection error. Please try again."
+    },
+    "branding": {
+      "tagline": "Modular workflow platform for your organization"
+    }
   },
   "header": {
     "search": "Search...",
     "userMenu": "User menu",
     "breadcrumb": {
       "home": "Home"
+    },
+    "logout": "Sign Out",
+    "role": {
+      "SUPER_ADMIN": "Super Admin",
+      "ADMIN": "Admin",
+      "USER": "User"
     }
   },
   "sidebar": {
@@ -23,13 +54,47 @@
     "categories": {
       "label": "Categories",
       "empty": "No modules"
-    }
+    },
+    "admin": "Administration",
+    "users": "Users",
+    "tenants": "Tenants"
   },
   "dashboard": {
     "title": "Dashboard",
     "empty": "No active widgets",
     "addWidget": "Add widget"
   },
+  "admin": {
+    "users": {
+      "title": "User Management",
+      "create": "Create User",
+      "edit": "Edit User",
+      "delete": "Delete User",
+      "deleteConfirm": "Are you sure you want to delete this user?",
+      "name": "Name",
+      "username": "Username",
+      "email": "Email",
+      "displayName": "Display Name",
+      "role": "Role",
+      "status": "Status",
+      "actions": "Actions",
+      "password": "Password",
+      "noUsers": "No users found"
+    },
+    "tenants": {
+      "title": "Tenant Management",
+      "create": "Create Tenant",
+      "edit": "Edit Tenant",
+      "name": "Name",
+      "slug": "Slug",
+      "status": "Status",
+      "userCount": "Users",
+      "actions": "Actions",
+      "noTenants": "No tenants found",
+      "deleteConfirm": "Are you sure you want to delete this tenant?",
+      "cannotDeleteActive": "Cannot delete tenants with active users"
+    }
+  },
   "theme": {
     "light": "Light",
     "dark": "Dark",