修复优化引起的 demo bug

apps/im_app/lib/features/login/view/login_page.dart

@@ -15,13 +15,12 @@ class LoginPage extends ConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
+    // ref.watch 保持 loginViewModelProvider 存活（AutoDispose 需要至少一个监听者）
+    final state = ref.watch(loginViewModelProvider);
     final s = context.styles;
 
     return Scaffold(
-      appBar: AppBar(
-        title: const Text('登录'),
-        automaticallyImplyLeading: false,
-      ),
+      appBar: AppBar(title: const Text('登录'), automaticallyImplyLeading: false),
       body: Center(
         child: Column(
           mainAxisSize: MainAxisSize.min,
@@ -34,7 +33,9 @@ class LoginPage extends ConsumerWidget {
             ),
             const SizedBox(height: 32),
             FilledButton(
-              onPressed: () => ref.read(loginViewModelProvider.notifier).demoLogin(),
+              onPressed: state.isLoading
+                  ? null
+                  : () => ref.read(loginViewModelProvider.notifier).demoLogin(),
               child: const Text('登录'),
             ),
           ],