Fix expired session showing EmbeddedFallback instead of login page

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

frontend/src/components/AuthGate.tsx

@@ -12,30 +12,20 @@ export function useAuth() {
 
 export default function AuthGate({ children }: { children: React.ReactNode }) {
   const [user, setUser] = useState<User | null>(null)
-  const [error, setError] = useState<string | null>(null)
 
   useEffect(() => {
     fetch('/api/auth/verify?app=maintenance', { credentials: 'include' })
       .then(r => {
-        if (r.status === 401 || r.status === 403) {
-          window.location.href = `/portal?redirect=${encodeURIComponent(window.location.href)}`
+        if (!r.ok) {
+          ;(window.top ?? window).location.href = '/login'
           return null
         }
-        if (!r.ok) throw new Error(`Auth check failed: ${r.status}`)
         return r.json()
       })
       .then(data => { if (data) setUser(data) })
-      .catch(err => setError(err.message))
+      .catch(() => { ;(window.top ?? window).location.href = '/login' })
   }, [])
 
-  if (error) {
-    return (
-      <div style={{ padding: 32, color: 'var(--danger)', fontFamily: 'var(--font)' }}>
-        Authentication error: {error}
-      </div>
-    )
-  }
-
   if (!user) {
     return (
       <div style={{