Phase 2: Tags UI, Custom Fields UI, Notifications Bell

- Tags UI: TagsPage (CRUD, color picker), TagBadge, TagSelector (multi-select, inline creation)
- Custom Fields Backend: model, schema, service, routes, migration 0041
- Custom Fields Frontend: CustomFieldsPage (definitions CRUD), CustomFieldRenderer (dynamic field rendering)
- Custom Fields: _collect_custom_field_definitions() extended to merge DB definitions with plugin definitions
- Notifications Bell: NotificationBell (30s polling, unread badge), NotificationDropdown, NotificationItem
- NotificationBell integrated into TopBar
- Routes: /tags, /settings/custom-fields registered
- Settings nav: Custom Fields entry added
- Menu items: Tags added to automation plugin manifest

frontend/src/api/notifications.ts

@@ -43,13 +43,14 @@ export function useNotifications() {
   });
 }
 
-export function useUnreadNotificationCount() {
+export function useUnreadNotificationCount(options?: { refetchInterval?: number }) {
   return useQuery({
     queryKey: ['notifications', 'unread-count'],
     queryFn: async () => {
       const data = await apiGet<UnreadCountResponse>('/notifications/unread-count');
       return data.count;
     },
+    refetchInterval: options?.refetchInterval,
   });
 }