refactor: stabilize app bootstrap and polling

lib/screens/remote_screen.dart

@@ -19,23 +19,22 @@ class RemoteScreen extends ConsumerStatefulWidget {
 }
 
 class _RemoteScreenState extends ConsumerState<RemoteScreen> {
-  bool _loading = true;
-
   @override
   void initState() {
     super.initState();
-    _bootstrap();
+    Future.microtask(() => ref.read(groupsProvider.notifier).startPolling());
   }
 
-  Future<void> _bootstrap() async {
-    await ref.read(groupsProvider.notifier).initAndRefresh();
-    await ref.read(authInfoProvider.notifier).load();
-    if (mounted) setState(() => _loading = false);
+  @override
+  void dispose() {
+    ref.read(groupsProvider.notifier).stopPolling();
+    super.dispose();
   }
 
   @override
   Widget build(BuildContext context) {
     final groups = ref.watch(groupsProvider);
+    final groupsLoadState = ref.watch(groupsLoadStateProvider);
     final currentHome = ref.watch(currentHomeProvider);
     final authInfo = ref.watch(authInfoProvider);
     final isAdmin = authInfo?['is_admin'] == true;
@@ -124,7 +123,7 @@ class _RemoteScreenState extends ConsumerState<RemoteScreen> {
           ),
         ],
       ),
-      body: _loading
+      body: groupsLoadState.isLoading && groups.isEmpty
           ? const Center(
               child: Column(
                 mainAxisAlignment: MainAxisAlignment.center,
@@ -138,6 +137,8 @@ class _RemoteScreenState extends ConsumerState<RemoteScreen> {
                 ],
               ),
             )
+          : groupsLoadState.hasError && groups.isEmpty
+          ? _GroupsErrorView(message: groupsLoadState.errorMessage)
           : groups.isEmpty
           ? Center(
               child: Column(
@@ -241,3 +242,48 @@ class _RemoteScreenState extends ConsumerState<RemoteScreen> {
     }
   }
 }
+
+class _GroupsErrorView extends ConsumerWidget {
+  final String? message;
+
+  const _GroupsErrorView({this.message});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    return Center(
+      child: Padding(
+        padding: const EdgeInsets.all(24),
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            const Icon(
+              Icons.wifi_off_rounded,
+              size: 64,
+              color: Colors.deepOrange,
+            ),
+            const SizedBox(height: 16),
+            const Text(
+              'Не удалось загрузить группы',
+              textAlign: TextAlign.center,
+              style: TextStyle(color: Colors.white70, fontSize: 16),
+            ),
+            if (message != null) ...[
+              const SizedBox(height: 8),
+              Text(
+                message!,
+                textAlign: TextAlign.center,
+                style: const TextStyle(color: Colors.white38, fontSize: 12),
+              ),
+            ],
+            const SizedBox(height: 16),
+            FilledButton.icon(
+              onPressed: () => ref.read(groupsProvider.notifier).refresh(),
+              icon: const Icon(Icons.refresh),
+              label: const Text('Повторить'),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}