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/core/auth/auth-gate.ts

@@ -3,6 +3,8 @@
  * @ai-context Prevents race conditions between IndexedDB init and API calls
  */
 
+import { useState, useEffect } from 'react';
+
 // Global authentication readiness state
 let authInitialized = false;
 let authInitPromise: Promise<void> | null = null;
@@ -99,4 +101,26 @@ const processRequestQueue = async () => {
 
   isProcessingQueue = false;
   console.log('[Auth Gate] Finished processing queued requests');
+};
+
+/**
+ * React hook to track auth initialization state
+ * Returns true once auth is fully initialized with token
+ */
+export const useIsAuthInitialized = () => {
+  const [initialized, setInitialized] = useState(authInitialized);
+
+  useEffect(() => {
+    if (authInitialized) {
+      setInitialized(true);
+      return;
+    }
+
+    // Wait for auth to initialize
+    waitForAuthInit().then(() => {
+      setInitialized(true);
+    });
+  }, []);
+
+  return initialized;
 };