feat: A3 数据层 AppCatalogController（feed/详情/分类加载，供页面切换）

lib/core/data/services/app_catalog_controller.dart

@@ -0,0 +1,39 @@
+// Author: fruit.com.cn
+
+import 'package:flutter/foundation.dart';
+
+import '../models/app_catalog.dart';
+import '../repositories/http_catalog_repository.dart';
+
+/// 首页/发现页 feed 状态（A3 数据层）。
+class AppCatalogController extends ChangeNotifier {
+  AppCatalogController(this._repository);
+
+  final HttpCatalogRepository _repository;
+
+  AppFeed? feed;
+  bool loading = false;
+  String? error;
+
+  Future<void> loadFeed() async {
+    loading = true;
+    error = null;
+    notifyListeners();
+    try {
+      feed = await _repository.fetchHomeFeed();
+    } catch (e) {
+      error = e.toString();
+    } finally {
+      loading = false;
+      notifyListeners();
+    }
+  }
+
+  Future<AppDramaDetail> loadDetail(int id) {
+    return _repository.fetchDramaDetail(id);
+  }
+
+  Future<List<AppCategory>> loadCategories() {
+    return _repository.fetchCategories();
+  }
+}