feat(web): migrate notification inbox to React

Add the React notification route with cursor-based inbox and sent-message views, read receipts, filters, unread badges, and safe fallback links for functionality that remains in the legacy frontend.

web-react/src/app/App.tsx

@@ -9,6 +9,7 @@ const LoginPage = lazy(() => import('../pages/LoginPage'))
 const DashboardPage = lazy(() => import('../pages/DashboardPage'))
 const AccountPage = lazy(() => import('../pages/AccountPage'))
 const UsersPage = lazy(() => import('../pages/UsersPage'))
+const NotificationsPage = lazy(() => import('../pages/NotificationsPage'))
 const SsoCallbackPage = lazy(() => import('../pages/SsoCallbackPage'))
 const SsoBindPage = lazy(() => import('../pages/SsoBindPage'))
 const AppShell = lazy(() => import('../layout/AppShell'))
@@ -52,6 +53,7 @@ function AppRoutes() {
           <Route path="/dashboard" element={<DashboardPage />} />
           <Route path="/account" element={<AccountPage />} />
           <Route path="/users" element={<UsersPage />} />
+          <Route path="/notifications" element={<NotificationsPage />} />
           <Route path="/" element={<Navigate to="/dashboard" replace />} />
         </Route>
         <Route path="*" element={<Navigate to="/dashboard" replace />} />