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/accounts/accounts_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/widgets/async_value_view.dart';
 import '../../core/widgets/empty_state.dart';
 import '../../core/widgets/money_text.dart';
+import '../../core/widgets/stale_banner.dart';
 import 'providers.dart';
 
 const _roleOrder = [AccountRole.liquid, AccountRole.savings, AccountRole.investment, AccountRole.debt];
@@ -42,6 +44,7 @@ class AccountsPage extends ConsumerWidget {
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final accounts = ref.watch(accountsProvider);
+    final stale = oldestFetch([accounts.valueOrNull?.fetchedAt]);
 
     return Scaffold(
       appBar: AppBar(title: const Text('Счета')),
@@ -50,7 +53,8 @@ class AccountsPage extends ConsumerWidget {
         child: AsyncValueView(
           value: accounts,
           onRetry: () => ref.invalidate(accountsProvider),
-          data: (rows) {
+          data: (cached) {
+            final rows = cached.data;
             if (rows.isEmpty) {
               return ListView(
                 children: const [
@@ -66,6 +70,7 @@ class AccountsPage extends ConsumerWidget {
             return ListView(
               padding: const EdgeInsets.all(16),
               children: [
+                if (stale != null) StaleBanner(fetchedAt: stale),
                 for (final role in _roleOrder)
                   if (active.any((a) => a.role == role))
                     _RoleSection(

app/lib/features/accounts/providers.dart

@@ -2,15 +2,18 @@ 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';
 
-/// Every account, archived included — screens decide what to show.
-final accountsProvider = FutureProvider.autoDispose<List<AccountOut>>((ref) async {
+/// Every account, archived included — screens decide what to show. See
+/// `docs/ai/offline-cache.md`: Счета reads `.data` and shows the offline banner;
+/// `accountNamesProvider` and the other consumers (Транзакции, События) just unwrap `.data`.
+final accountsProvider = FutureProvider.autoDispose<Cached<List<AccountOut>>>((ref) async {
   final r = await ref.watch(apiProvider).getAccountsApi().accountsList();
-  return r.data ?? const [];
+  return Cached(r.data ?? const [], fetchedAt: r.extra['fetchedAt'] as DateTime?);
 });
 
 /// `account_id -> name`, for screens that only carry the id (transactions, rules).
 final accountNamesProvider = Provider.autoDispose<Map<int, String>>((ref) {
-  final accounts = ref.watch(accountsProvider).valueOrNull ?? const [];
+  final accounts = ref.watch(accountsProvider).valueOrNull?.data ?? const [];
   return {for (final a in accounts) a.id: a.name};
 });