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/routes/index.tsx

@@ -55,6 +55,8 @@ const CommunicationPage = React.lazy(() => import('@/pages/Communication').then(
 const WorkflowsPage = React.lazy(() => import('@/pages/Workflows').then(m => ({ default: m.WorkflowsPage })));
 const DedupMergePage = React.lazy(() => import('@/pages/DedupMerge').then(m => ({ default: m.DedupMergePage })));
 const ImportExportPage = React.lazy(() => import('@/pages/ImportExport').then(m => ({ default: m.ImportExportPage })));
+const TagsPage = React.lazy(() => import('@/pages/Tags').then(m => ({ default: m.TagsPage })));
+const CustomFieldsPage = React.lazy(() => import('@/pages/CustomFields').then(m => ({ default: m.CustomFieldsPage })));
 
 /** Centered spinner fallback for lazy-loaded routes */
 function PageLoader() {
@@ -131,6 +133,7 @@ const router = createBrowserRouter([
       { path: '/workflows', element: withSuspense(<WorkflowsPage />) },
       { path: '/contacts/dedup', element: withSuspense(<DedupMergePage />) },
       { path: '/import-export', element: withSuspense(<ImportExportPage />) },
+      { path: '/tags', element: withSuspense(<TagsPage />) },
       { path: '/profile', element: withSuspense(<SettingsProfilePage />) },
       {
         path: '/settings',
@@ -155,6 +158,7 @@ const router = createBrowserRouter([
           { path: 'mcp', element: withSuspense(<SettingsMcpPage />) },
           { path: 'ai-settings', element: withSuspense(<SettingsAIPage />) },
           { path: 'menu', element: withSuspense(<SettingsMenuOrderPage />) },
+          { path: 'custom-fields', element: withSuspense(<CustomFieldsPage />) },
           { path: '*', element: <PluginRouteRenderer /> },
         ],
       },