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/goals/data/goals_api.dart

@@ -11,6 +11,7 @@ library;
 
 import 'package:dio/dio.dart';
 
+import '../../../core/cache/cached.dart';
 import '../../../core/utils/json.dart';
 
 class Goal {
@@ -125,11 +126,14 @@ class GoalsApi {
 
   static const _base = '/api/v1/goals';
 
-  Future<List<Goal>> list() async {
+  /// See `docs/ai/offline-cache.md`: this hand-written client returns `Cached<T>` directly
+  /// (there is no generated `Response<T>` for `GoalsPage` to unwrap `r.cached` from).
+  Future<Cached<List<Goal>>> list() async {
     final r = await _dio.get<List<dynamic>>(_base);
-    return (r.data ?? const [])
+    final goals = (r.data ?? const [])
         .map((e) => Goal.fromJson(Map<String, dynamic>.from(e as Map)))
         .toList();
+    return Cached(goals, fetchedAt: r.extra['fetchedAt'] as DateTime?);
   }
 
   Future<Goal> create(Goal goal) async {
@@ -144,8 +148,11 @@ class GoalsApi {
 
   Future<void> delete(int id) => _dio.delete<void>('$_base/$id');
 
-  Future<GoalProgress> progress(int id) async {
+  Future<Cached<GoalProgress>> progress(int id) async {
     final r = await _dio.get<Map<String, dynamic>>('$_base/$id/progress');
-    return GoalProgress.fromJson(r.data ?? const {});
+    return Cached(
+      GoalProgress.fromJson(r.data ?? const {}),
+      fetchedAt: r.extra['fetchedAt'] as DateTime?,
+    );
   }
 }