feat(05-01): settings shell, header link, and i18n keys for dashboard phase

- Create settings/layout.tsx with SettingsSidebar and back-to-dashboard link
- Create settings/page.tsx with redirect to /settings/dashboard
- Create settings-sidebar.tsx with Widgets and Calendar nav items, aria-current
- Add Settings link in header user dropdown (gear icon, before logout)
- Add settings namespace (DE+EN) with all category and action keys
- Add widgets namespace (DE+EN) with all widget names, descriptions, error states
- Add header.settings key ("Einstellungen"/"Settings")

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

apps/web/src/messages/en.json

@@ -67,6 +67,7 @@
     "breadcrumb": {
       "home": "Home"
     },
+    "settings": "Settings",
     "logout": "Sign Out",
     "role": {
       "SUPER_ADMIN": "Super Admin",
@@ -98,6 +99,48 @@
     "empty": "No active widgets",
     "addWidget": "Add widget"
   },
+  "settings": {
+    "link": "Settings",
+    "navLabel": "Settings",
+    "backToDashboard": "Back to Dashboard",
+    "categoryDashboard": "Dashboard",
+    "categoryWidgets": "Widgets",
+    "categoryCalendar": "Calendar",
+    "sourceDeleteConfirm": "Are you sure you want to delete this calendar source?",
+    "sourceDeleteCta": "Delete source",
+    "providerDeleteConfirm": "Are you sure you want to delete this search provider?",
+    "providerDeleteCta": "Delete provider",
+    "cancel": "Cancel"
+  },
+  "widgets": {
+    "emptyHeading": "No active widgets",
+    "emptyBody": "Click edit to add widgets to your dashboard.",
+    "addWidget": "Add widget",
+    "catalogTitle": "Add widget",
+    "deleteTooltip": "Remove widget",
+    "editMode": "Edit dashboard",
+    "saveChanges": "Save changes",
+    "layoutLoadError": "Could not load dashboard. Please reload the page.",
+    "widgetSaveError": "Could not save changes. Please try again.",
+    "clock.name": "Clock",
+    "clock.description": "Shows the current time",
+    "clock.dateHint": "Show date",
+    "search.name": "Search",
+    "search.description": "Quick web search",
+    "search.placeholder": "Search...",
+    "calendar.name": "Calendar",
+    "calendar.description": "Upcoming events",
+    "calendar.emptyNoSources": "No calendar sources configured",
+    "calendar.emptyNoEvents": "No upcoming events",
+    "calendar.connectionSuccess": "Connection successful",
+    "calendar.connectionError": "Connection failed. Please check the URL and credentials.",
+    "calendar.addSource": "Add source",
+    "calendar.sourceEmpty": "No calendar sources configured. Add a source to display events.",
+    "note.name": "Notes",
+    "note.description": "Free-text notes with Markdown",
+    "note.defaultTitle": "Note",
+    "note.autosaveError": "Save failed"
+  },
   "admin": {
     "users": {
       "title": "User Management",