feat: surface read-only load errors

lib/screens/stats_screen.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../app/load_state.dart';
 import '../providers/providers.dart';
+import '../widgets/load_error_view.dart';
 
 /// Экран просмотра статистики.
 /// Показывает сводку по группам за выбранный период.
@@ -12,7 +14,6 @@ class StatsScreen extends ConsumerStatefulWidget {
 }
 
 class _StatsScreenState extends ConsumerState<StatsScreen> {
-  bool _loading = true;
   int _days = 7;
 
   @override
@@ -22,14 +23,13 @@ class _StatsScreenState extends ConsumerState<StatsScreen> {
   }
 
   Future<void> _load() async {
-    setState(() => _loading = true);
     await ref.read(statsProvider.notifier).load(days: _days);
-    if (mounted) setState(() => _loading = false);
   }
 
   @override
   Widget build(BuildContext context) {
-    final stats = ref.watch(statsProvider);
+    final statsState = ref.watch(statsProvider);
+    final stats = statsState.data;
     final groups = (stats['groups'] as List<dynamic>?) ?? [];
 
     return Scaffold(
@@ -62,37 +62,70 @@ class _StatsScreenState extends ConsumerState<StatsScreen> {
           ),
 
           // ─── Содержимое ───
-          Expanded(
-            child: _loading
-                ? const Center(
-                    child: CircularProgressIndicator(color: Colors.deepOrange),
-                  )
-                : groups.isEmpty
-                ? const Center(
-                    child: Text(
-                      'Нет данных',
-                      style: TextStyle(color: Colors.white54),
-                    ),
-                  )
-                : RefreshIndicator(
-                    color: Colors.deepOrange,
-                    onRefresh: _load,
-                    child: ListView.builder(
-                      padding: const EdgeInsets.all(12),
-                      itemCount: groups.length,
-                      itemBuilder: (context, index) {
-                        final g = groups[index];
-                        return _StatsCard(
-                          data: g is Map ? Map<String, dynamic>.from(g) : {},
-                        );
-                      },
-                    ),
-                  ),
-          ),
+          Expanded(child: _buildContent(statsState, groups)),
         ],
       ),
     );
   }
+
+  Widget _buildContent(
+    LoadState<Map<String, dynamic>> statsState,
+    List<dynamic> groups,
+  ) {
+    if ((statsState.isIdle || statsState.isLoading) && groups.isEmpty) {
+      return const Center(
+        child: CircularProgressIndicator(color: Colors.deepOrange),
+      );
+    }
+
+    if (statsState.hasError && groups.isEmpty) {
+      return LoadErrorView(
+        title: 'Не удалось загрузить статистику',
+        message: statsState.errorMessage,
+        icon: Icons.bar_chart,
+        onRetry: _load,
+      );
+    }
+
+    if (groups.isEmpty) {
+      return const Center(
+        child: Text('Нет данных', style: TextStyle(color: Colors.white54)),
+      );
+    }
+
+    final hasStatusHeader = statsState.isLoading || statsState.hasError;
+    final statusHeaderCount = hasStatusHeader ? 1 : 0;
+
+    return RefreshIndicator(
+      color: Colors.deepOrange,
+      onRefresh: _load,
+      child: ListView.builder(
+        physics: const AlwaysScrollableScrollPhysics(),
+        padding: const EdgeInsets.all(12),
+        itemCount: groups.length + statusHeaderCount,
+        itemBuilder: (context, index) {
+          if (hasStatusHeader && index == 0) {
+            if (statsState.isLoading) {
+              return const Padding(
+                padding: EdgeInsets.only(bottom: 12),
+                child: LinearProgressIndicator(color: Colors.deepOrange),
+              );
+            }
+
+            return LoadErrorBanner(
+              title: 'Не удалось обновить статистику',
+              message: statsState.errorMessage,
+              onRetry: _load,
+            );
+          }
+
+          final groupIndex = index - statusHeaderCount;
+          final g = groups[groupIndex];
+          return _StatsCard(data: g is Map ? Map<String, dynamic>.from(g) : {});
+        },
+      ),
+    );
+  }
 }
 
 /// Карточка статистики одной группы