fix: correct generate endpoint return type, migration server_default SQL, and auth loading propagation

frontend/src/store/auth.ts

@@ -10,20 +10,22 @@ export interface User {
 
 // Simple module-level state (no external lib needed)
 let currentUser: User | null = null
+let isLoading = true
+let fetchPromise: Promise<void> | null = null
 const listeners = new Set<() => void>()
 
 export function useAuth() {
   const [user, setUser] = useState<User | null>(currentUser)
-  const [loading, setLoading] = useState(currentUser === null)
+  const [loading, setLoading] = useState(isLoading)
 
   useEffect(() => {
-    const update = () => setUser(currentUser)
+    const update = () => { setUser(currentUser); setLoading(isLoading) }
     listeners.add(update)
-    if (currentUser === null) {
-      authApi.me()
-        .then((res) => { currentUser = res.data; listeners.forEach((l) => l()) })
-        .catch(() => { currentUser = null; listeners.forEach((l) => l()) })
-        .finally(() => setLoading(false))
+    if (!fetchPromise) {
+      fetchPromise = authApi.me()
+        .then((res) => { currentUser = res.data })
+        .catch(() => { currentUser = null })
+        .finally(() => { isLoading = false; listeners.forEach((l) => l()) })
     }
     return () => { listeners.delete(update) }
   }, [])