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/income/data/income_api.dart

@@ -11,6 +11,7 @@ library;
 
 import 'package:dio/dio.dart';
 
+import '../../../core/cache/cached.dart';
 import '../../../core/utils/json.dart';
 
 /// One expected (or already paid) payment.
@@ -205,7 +206,9 @@ class IncomeApi {
 
   static const _base = '/api/v1/income';
 
-  Future<IncomeCalendar> calendar({
+  /// See `docs/ai/offline-cache.md`: this hand-written client returns `Cached<T>` directly
+  /// (there is no generated `Response<T>` for the screen to unwrap `r.cached` from).
+  Future<Cached<IncomeCalendar>> calendar({
     String scope = 'all',
     DateTime? dateFrom,
     DateTime? dateTo,
@@ -217,10 +220,13 @@ class IncomeApi {
       'date_to': ?_isoDate(dateTo),
       'include_paid': includePaid,
     });
-    return IncomeCalendar.fromJson(r.data ?? const {});
+    return Cached(
+      IncomeCalendar.fromJson(r.data ?? const {}),
+      fetchedAt: r.extra['fetchedAt'] as DateTime?,
+    );
   }
 
-  Future<IncomeHistory> history({
+  Future<Cached<IncomeHistory>> history({
     String scope = 'all',
     String group = 'month',
     DateTime? dateFrom,
@@ -234,15 +240,21 @@ class IncomeApi {
       'date_to': ?_isoDate(dateTo),
       'kind': ?kind,
     });
-    return IncomeHistory.fromJson(r.data ?? const {});
+    return Cached(
+      IncomeHistory.fromJson(r.data ?? const {}),
+      fetchedAt: r.extra['fetchedAt'] as DateTime?,
+    );
   }
 
-  Future<IncomeForecast> forecast({String scope = 'all', int months = 12}) async {
+  Future<Cached<IncomeForecast>> forecast({String scope = 'all', int months = 12}) async {
     final r = await _dio.get<Map<String, dynamic>>('$_base/forecast', queryParameters: {
       'scope': scope,
       'months': months,
     });
-    return IncomeForecast.fromJson(r.data ?? const {});
+    return Cached(
+      IncomeForecast.fromJson(r.data ?? const {}),
+      fetchedAt: r.extra['fetchedAt'] as DateTime?,
+    );
   }
 
   /// `format: date` on the wire. `DateQueryInterceptor` does this for the generated client;