feat: add in-app notification system with real-time delivery

Introduces a full in-app notification system with three types (simple,
boolean with server-side callbacks, navigate), three scopes (user, trip,
admin), fan-out persistence per recipient, and real-time push via
WebSocket. Includes a notification bell in the navbar, dropdown, dedicated
/notifications page, and a dev-only admin tab for testing all notification
variants.

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

client/src/App.tsx

@@ -11,10 +11,12 @@ import SettingsPage from './pages/SettingsPage'
 import VacayPage from './pages/VacayPage'
 import AtlasPage from './pages/AtlasPage'
 import SharedTripPage from './pages/SharedTripPage'
+import NotificationsPage from './pages/NotificationsPage'
 import { ToastContainer } from './components/shared/Toast'
 import { TranslationProvider, useTranslation } from './i18n'
 import { authApi } from './api/client'
 import { usePermissionsStore, PermissionLevel } from './store/permissionsStore'
+import { useNotificationListener } from './hooks/useNotificationListener'
 
 interface ProtectedRouteProps {
   children: ReactNode
@@ -75,15 +77,16 @@ function RootRedirect() {
 }
 
 export default function App() {
-  const { loadUser, isAuthenticated, demoMode, setDemoMode, setHasMapsKey, setServerTimezone, setAppRequireMfa, setTripRemindersEnabled } = useAuthStore()
+  const { loadUser, isAuthenticated, demoMode, setDemoMode, setDevMode, setHasMapsKey, setServerTimezone, setAppRequireMfa, setTripRemindersEnabled } = useAuthStore()
   const { loadSettings } = useSettingsStore()
 
   useEffect(() => {
     if (!location.pathname.startsWith('/shared/')) {
       loadUser()
     }
-    authApi.getAppConfig().then(async (config: { demo_mode?: boolean; has_maps_key?: boolean; version?: string; timezone?: string; require_mfa?: boolean; trip_reminders_enabled?: boolean; permissions?: Record<string, PermissionLevel> }) => {
+    authApi.getAppConfig().then(async (config: { demo_mode?: boolean; dev_mode?: boolean; has_maps_key?: boolean; version?: string; timezone?: string; require_mfa?: boolean; trip_reminders_enabled?: boolean; permissions?: Record<string, PermissionLevel> }) => {
       if (config?.demo_mode) setDemoMode(true)
+      if (config?.dev_mode) setDevMode(true)
       if (config?.has_maps_key !== undefined) setHasMapsKey(config.has_maps_key)
       if (config?.timezone) setServerTimezone(config.timezone)
       if (config?.require_mfa !== undefined) setAppRequireMfa(!!config.require_mfa)
@@ -114,6 +117,8 @@ export default function App() {
 
   const { settings } = useSettingsStore()
 
+  useNotificationListener()
+
   useEffect(() => {
     if (isAuthenticated) {
       loadSettings()
@@ -213,6 +218,14 @@ export default function App() {
             </ProtectedRoute>
           }
         />
+        <Route
+          path="/notifications"
+          element={
+            <ProtectedRoute>
+              <NotificationsPage />
+            </ProtectedRoute>
+          }
+        />
         <Route path="*" element={<Navigate to="/" replace />} />
       </Routes>
     </TranslationProvider>