fix(api): handle 401 responses by redirecting to login

frontend/lib/api.ts

@@ -1,3 +1,4 @@
+import { redirect } from 'next/navigation';
 import { getAuthHeaders } from './auth-headers';
 
 const API_BASE =
@@ -23,6 +24,9 @@ export async function fetchJson<T>(path: string, init?: RequestInit): Promise<T>
   });
 
   if (!res.ok) {
+    if (res.status === 401 && isServer) {
+      redirect('/login');
+    }
     const text = await res.text();
     throw new Error(`API ${res.status}: ${text}`);
   }