feat(app): offline-кэш GET-запросов на дашборде — фаза 5

CacheInterceptor кэширует каждый успешный GET по путь+параметры в drift
(sqlite нативно, wasm+OPFS в браузере) и подменяет им сетевую ошибку;
провайдер отдаёт Cached<T>, экран показывает баннер «данные на …».
Контракт для остальных экранов — docs/ai/offline-cache.md.

flake.nix: libsecret/pkg-config для линуксовой сборки, jq/curl для
just app-web-assets (сборка sqlite3.wasm + drift_worker.js).

app/test/home_page_test.dart

@@ -1,4 +1,5 @@
 import 'package:fintracker_api/fintracker_api.dart';
+import 'package:fintracker_app/core/cache/cached.dart';
 import 'package:fintracker_app/core/widgets/money_text.dart';
 import 'package:fintracker_app/features/home/home_page.dart';
 import 'package:fintracker_app/features/home/providers.dart';
@@ -6,9 +7,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-void main() {
-  testWidgets('Обзор renders stat tiles from a net worth breakdown', (tester) async {
-    final breakdown = NetWorthBreakdown(
+NetWorthBreakdown _breakdown() => NetWorthBreakdown(
       accounts: const [],
       byCurrency: const {'RUB': '123456.78'},
       d: DateTime(2026, 9, 17),
@@ -20,22 +19,33 @@ void main() {
       totalRub: '123456.78',
     );
 
+RunwayOut _runway() => RunwayOut(
+      asOf: DateTime(2026, 9, 17),
+      avgBaseline3mRub: '0',
+      liquidReserveRub: '0',
+      runwayMonths: null,
+    );
+
+// Every provider HomePage watches needs an override — including
+// portfolioSummaryHomeProvider, easy to forget since it renders nothing on an
+// empty ledger. Without it, HomePage falls through to the real apiProvider,
+// which now also opens a real ResponseCacheDatabase (see docs/ai/offline-cache.md).
+List<Override> _overrides({DateTime? staleAt}) => [
+      netWorthBreakdownProvider.overrideWith((ref) => Cached(_breakdown(), fetchedAt: staleAt)),
+      netWorthSeriesProvider.overrideWith((ref) => Cached(const <NetWorthDay>[], fetchedAt: staleAt)),
+      cashflowThisMonthProvider.overrideWith((ref) => Cached(null, fetchedAt: staleAt)),
+      cashflowLast12Provider.overrideWith((ref) => Cached(const <CashFlowMonth>[], fetchedAt: staleAt)),
+      runwayProvider.overrideWith((ref) => Cached(_runway(), fetchedAt: staleAt)),
+      metricsStatusProvider.overrideWith((ref) => Cached(null, fetchedAt: staleAt)),
+      dataQualityProvider.overrideWith((ref) => Cached(const <DataQualityRow>[], fetchedAt: staleAt)),
+      portfolioSummaryHomeProvider.overrideWith((ref) => Cached(null, fetchedAt: staleAt)),
+    ];
+
+void main() {
+  testWidgets('Обзор renders stat tiles from a net worth breakdown', (tester) async {
     await tester.pumpWidget(
       ProviderScope(
-        overrides: [
-          netWorthBreakdownProvider.overrideWith((ref) => breakdown),
-          netWorthSeriesProvider.overrideWith((ref) => const <NetWorthDay>[]),
-          cashflowThisMonthProvider.overrideWith((ref) => null),
-          cashflowLast12Provider.overrideWith((ref) => const <CashFlowMonth>[]),
-          runwayProvider.overrideWith((ref) => RunwayOut(
-                asOf: DateTime(2026, 9, 17),
-                avgBaseline3mRub: '0',
-                liquidReserveRub: '0',
-                runwayMonths: null,
-              )),
-          metricsStatusProvider.overrideWith((ref) => null),
-          dataQualityProvider.overrideWith((ref) => const <DataQualityRow>[]),
-        ],
+        overrides: _overrides(),
         child: const MaterialApp(home: HomePage()),
       ),
     );
@@ -47,5 +57,18 @@ void main() {
     expect(find.text(MoneyText.format('3000', 'RUB')), findsOneWidget);
     expect(find.text('Долги'), findsOneWidget);
     expect(find.text(MoneyText.format('1000', 'RUB')), findsOneWidget);
+    expect(find.textContaining('Нет соединения'), findsNothing);
+  });
+
+  testWidgets('shows the offline banner when the dashboard came from the cache', (tester) async {
+    await tester.pumpWidget(
+      ProviderScope(
+        overrides: _overrides(staleAt: DateTime(2026, 9, 10, 8, 30)),
+        child: const MaterialApp(home: HomePage()),
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    expect(find.textContaining('Нет соединения — данные на 10.09.2026 08:30'), findsOneWidget);
   });
 }