Fix blank stations page by waiting for auth initialization

- Add useIsAuthInitialized hook to auth-gate for reactive auth state
  - Returns true once auth token is acquired and ready
  - Waits for waitForAuthInit() promise to resolve

- Update useSavedStations hook to wait for auth before fetching
  - Add 'enabled: isAuthInitialized' to useQuery config
  - Prevents 401 errors from requests made before token is ready
  - Fixes race condition where hook fires before interceptor is set up

The stations page was blank because useSavedStations() made an API call
with refetchOnMount:true before the auth token interceptor was added,
causing a 401 response that made the component unmount/remount, creating
a React DOM error in the error boundary.

Now the hook waits for isAuthInitialized to be true before making the
initial API call, ensuring the token interceptor is ready.

🤖 Generated with Claude Code

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

frontend/src/features/stations/hooks/useSavedStations.ts

@@ -3,6 +3,7 @@
  */
 
 import { useQuery, useQueryClient } from '@tanstack/react-query';
+import { useIsAuthInitialized } from '../../../core/auth/auth-gate';
 import { stationsApi } from '../api/stations.api';
 import { SavedStation } from '../types/stations.types';
 
@@ -33,12 +34,15 @@ interface UseSavedStationsOptions {
  * ```
  */
 export function useSavedStations(options?: UseSavedStationsOptions) {
+  const isAuthInitialized = useIsAuthInitialized();
+
   return useQuery({
     queryKey: SAVED_STATIONS_QUERY_KEY,
     queryFn: () => stationsApi.getSavedStations(),
     staleTime: options?.staleTime ?? 5 * 60 * 1000, // 5 minutes default
     refetchOnWindowFocus: options?.refetchOnWindowFocus ?? true,
-    refetchOnMount: true
+    refetchOnMount: true,
+    enabled: isAuthInitialized // Only fetch once auth is initialized
   });
 }