feat(flutter): 重构四 Tab 与浏览页

lib/pages/discover/discover_logic.dart

@@ -28,6 +28,8 @@ class DiscoverLogic extends ChangeNotifier {
   String _lastRequestedQuery = '';
   int _searchRequest = 0;
   bool _disposed = false;
+  TheaterLanguage language = TheaterLanguage.all;
+  String? selectedCategoryId;
 
   bool get hasSearchQuery => search.text.trim().isNotEmpty;
 
@@ -48,6 +50,20 @@ class DiscoverLogic extends ChangeNotifier {
 
   void openSearch() => searchFocus.requestFocus();
 
+  /// Selects a language for the visual filter state.
+  void selectLanguage(TheaterLanguage value) {
+    if (language == value) return;
+    language = value;
+    notify();
+  }
+
+  /// Selects one category chip; null represents all categories.
+  void selectCategory(String? categoryId) {
+    if (selectedCategoryId == categoryId) return;
+    selectedCategoryId = categoryId;
+    notify();
+  }
+
   void retrySearch() {
     final query = search.text.trim();
     if (query.isNotEmpty) unawaited(_runSearch(query));