feat(app): экраны импорта отчётов, целей, доходов, ребалансировки, налогов и бенчмарков

Импорт (/imports, /instruments/pending) и фаза 4 (/goals, /income,
/rebalance, /tax, аналитика-хаб с benchmarks_card) — по
docs/ai/import-contract.md и docs/ai/phase4-contract.md. file_picker для
загрузки отчёта.

app/lib/features/tax/providers.dart

@@ -0,0 +1,30 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../../core/api/api_client.dart';
+import 'data/tax_api.dart';
+
+final taxApiProvider = Provider<TaxApi>((ref) => TaxApi(ref.watch(apiProvider).dio));
+
+final taxYearProvider = StateProvider<int>((ref) => DateTime.now().year);
+
+/// Optional account filter; null = all accounts.
+final taxAccountProvider = StateProvider<int?>((ref) => null);
+
+final taxSummaryProvider = FutureProvider.autoDispose<TaxSummary>((ref) async {
+  return ref.watch(taxApiProvider).summary(
+        year: ref.watch(taxYearProvider),
+        accountId: ref.watch(taxAccountProvider),
+      );
+});
+
+final taxLotsProvider = FutureProvider.autoDispose<List<TaxLot>>((ref) async {
+  return ref.watch(taxApiProvider).lots(
+        year: ref.watch(taxYearProvider),
+        accountId: ref.watch(taxAccountProvider),
+      );
+});
+
+void invalidateTaxProviders(WidgetRef ref) {
+  ref.invalidate(taxSummaryProvider);
+  ref.invalidate(taxLotsProvider);
+}