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/rebalance/data/rebalance_api.dart

@@ -12,6 +12,7 @@ library;
 import 'package:decimal/decimal.dart';
 import 'package:dio/dio.dart';
 
+import '../../../core/cache/cached.dart';
 import '../../../core/utils/json.dart';
 
 /// The dimensions targets can be set along, as wire strings (`AssetClass` is never exposed
@@ -214,12 +215,14 @@ class RebalanceApi {
   /// is per-dimension, so the set has to be addressable per-dimension as well. Sending
   /// `dimension` is harmless for a server that ignores it and necessary for one that does
   /// not — revisit once the route is in the spec.
-  Future<TargetSet> getTargets(int portfolioId, {String dimension = 'asset_class'}) async {
+  /// 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<TargetSet>> getTargets(int portfolioId, {String dimension = 'asset_class'}) async {
     final r = await _dio.get<Map<String, dynamic>>(
       '$_base/$portfolioId/targets',
       queryParameters: {'dimension': dimension},
     );
-    return TargetSet.fromJson(r.data ?? const {});
+    return Cached(TargetSet.fromJson(r.data ?? const {}), fetchedAt: r.extra['fetchedAt'] as DateTime?);
   }
 
   /// Full replacement of one dimension — partial updates are not supported by the contract.
@@ -231,7 +234,7 @@ class RebalanceApi {
     return TargetSet.fromJson(r.data ?? const {});
   }
 
-  Future<RebalancePlan> plan(
+  Future<Cached<RebalancePlan>> plan(
     int portfolioId, {
     String dimension = 'asset_class',
     String? cashAvailable,
@@ -240,6 +243,9 @@ class RebalanceApi {
       '$_base/$portfolioId/rebalance',
       queryParameters: {'dimension': dimension, 'cash_available': ?cashAvailable},
     );
-    return RebalancePlan.fromJson(r.data ?? const {});
+    return Cached(
+      RebalancePlan.fromJson(r.data ?? const {}),
+      fetchedAt: r.extra['fetchedAt'] as DateTime?,
+    );
   }
 }