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/cashflow/cashflow_page.dart

@@ -5,11 +5,13 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
+import '../../core/cache/cached.dart';
 import '../../core/theme/chart_colors.dart';
 import '../../core/utils/ru_date.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 _incomeColor = ChartColors.income;
@@ -26,6 +28,7 @@ class CashflowPage extends ConsumerWidget {
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final monthly = ref.watch(cashflowMonthly24Provider);
+    final stale = oldestFetch([monthly.valueOrNull?.fetchedAt]);
 
     return Scaffold(
       appBar: AppBar(title: const Text('Потоки')),
@@ -34,7 +37,8 @@ class CashflowPage extends ConsumerWidget {
         child: AsyncValueView(
           value: monthly,
           onRetry: () => ref.invalidate(cashflowMonthly24Provider),
-          data: (rows) {
+          data: (cached) {
+            final rows = cached.data;
             if (rows.isEmpty) {
               return ListView(
                 children: const [
@@ -48,6 +52,7 @@ class CashflowPage extends ConsumerWidget {
             return ListView(
               padding: const EdgeInsets.all(16),
               children: [
+                if (stale != null) StaleBanner(fetchedAt: stale),
                 const _Legend(),
                 const SizedBox(height: 8),
                 SizedBox(

app/lib/features/cashflow/providers.dart

@@ -2,9 +2,10 @@ 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';
 
-/// The last 24 months, oldest first (as the API returns them).
-final cashflowMonthly24Provider = FutureProvider.autoDispose<List<CashFlowMonth>>((ref) async {
+/// The last 24 months, oldest first (as the API returns them). See `docs/ai/offline-cache.md`.
+final cashflowMonthly24Provider = FutureProvider.autoDispose<Cached<List<CashFlowMonth>>>((ref) async {
   final r = await ref.watch(apiProvider).getCashflowApi().cashflowMonthly(months: 24);
-  return r.data ?? const [];
+  return Cached(r.data ?? const [], fetchedAt: r.extra['fetchedAt'] as DateTime?);
 });