feat(05-02): add widget settings panel with search provider form

- Settings > Dashboard page with per-widget-instance config
- Clock config: timezone select (IANA list) + date toggle (D-12/D-13)
- Note config: editable title field (D-17)
- Search config: SearchProviderForm with add/delete and {query} validation (D-15)
- Calendar config: link to calendar-specific settings
- i18n keys for search provider management (en + de)
- Fix useRef initialization for React 19 strict mode (note-widget)
- Fix unknown type narrowing in widget title display

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

apps/web/src/messages/en.json

@@ -139,7 +139,10 @@
     "note.name": "Notes",
     "note.description": "Free-text notes with Markdown",
     "note.defaultTitle": "Note",
-    "note.autosaveError": "Save failed"
+    "note.autosaveError": "Save failed",
+    "search.providers": "Search Providers",
+    "search.addProvider": "Add Custom Provider",
+    "search.addProviderButton": "Add Provider"
   },
   "admin": {
     "users": {