feat(app): offline-кэш на остальных экранах — фаза 5

accounts, cashflow, categories, goals, income, portfolio (+instrument),
rebalance, tax, rules переведены на Cached<T> по контракту
docs/ai/offline-cache.md. Общие/второстепенные селекторы (scopesProvider,
categoriesListProvider и т.п.) оставлены как есть — не основной контент
экрана. sync_page.dart и settings_page.dart не тронуты (первый — заменён
health-page отдельно, второй — чистые действия без списка для баннера).

app/lib/features/rules/providers.dart

@@ -2,19 +2,23 @@ import 'package:fintracker_api/fintracker_api.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../../core/api/api_client.dart';
+import '../../core/cache/cached.dart';
 
-final rulesListProvider = FutureProvider.autoDispose<List<RuleOut>>((ref) async {
+/// See `docs/ai/offline-cache.md`.
+final rulesListProvider = FutureProvider.autoDispose<Cached<List<RuleOut>>>((ref) async {
   final r = await ref.watch(apiProvider).getRulesApi().rulesList();
-  return r.data ?? const [];
+  return Cached(r.data ?? const [], fetchedAt: r.extra['fetchedAt'] as DateTime?);
 });
 
-/// Enabled rules that matched nothing in the latest refresh.
-final rulesStaleProvider = FutureProvider.autoDispose<List<RuleOut>>((ref) async {
+/// Enabled rules that matched nothing in the latest refresh — «устарело» here is a business
+/// concept (the rule looks dead), unrelated to the offline-cache staleness this file also
+/// tracks; both happen to be named "stale" in their own domains.
+final rulesStaleProvider = FutureProvider.autoDispose<Cached<List<RuleOut>>>((ref) async {
   final r = await ref.watch(apiProvider).getRulesApi().rulesStale();
-  return r.data ?? const [];
+  return Cached(r.data ?? const [], fetchedAt: r.extra['fetchedAt'] as DateTime?);
 });
 
 final staleRuleIdsProvider = Provider.autoDispose<Set<int>>((ref) {
-  final stale = ref.watch(rulesStaleProvider).valueOrNull ?? const [];
+  final stale = ref.watch(rulesStaleProvider).valueOrNull?.data ?? const [];
   return {for (final r in stale) r.id};
 });

app/lib/features/rules/rules_page.dart

@@ -5,9 +5,11 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../../core/api/api_client.dart';
 import '../../core/auth/auth_controller.dart';
+import '../../core/cache/cached.dart';
 import '../../core/utils/ru_date.dart';
 import '../../core/widgets/async_value_view.dart';
 import '../../core/widgets/empty_state.dart';
+import '../../core/widgets/stale_banner.dart';
 import 'providers.dart';
 
 String ruleKindLabel(RuleKind k) => switch (k) {
@@ -77,6 +79,10 @@ class RulesPage extends ConsumerWidget {
   Widget build(BuildContext context, WidgetRef ref) {
     final rules = ref.watch(rulesListProvider);
     final staleIds = ref.watch(staleRuleIdsProvider);
+    final stale = oldestFetch([
+      rules.valueOrNull?.fetchedAt,
+      ref.watch(rulesStaleProvider).valueOrNull?.fetchedAt,
+    ]);
 
     return Scaffold(
       appBar: AppBar(
@@ -101,11 +107,13 @@ class RulesPage extends ConsumerWidget {
         child: AsyncValueView(
           value: rules,
           onRetry: () => ref.invalidate(rulesListProvider),
-          data: (rows) {
+          data: (cached) {
+            final rows = cached.data;
             if (rows.isEmpty) {
               return ListView(
-                children: const [
-                  EmptyState(icon: Icons.rule_folder_outlined, message: 'Правил ещё нет.'),
+                children: [
+                  if (stale != null) StaleBanner(fetchedAt: stale),
+                  const EmptyState(icon: Icons.rule_folder_outlined, message: 'Правил ещё нет.'),
                 ],
               );
             }
@@ -113,6 +121,7 @@ class RulesPage extends ConsumerWidget {
             return ListView(
               padding: const EdgeInsets.all(16),
               children: [
+                if (stale != null) StaleBanner(fetchedAt: stale),
                 for (final rule in sorted)
                   _RuleTile(
                     rule: rule,