update cart/favorite

lib/features/favorites/data/datasources/favorite_products_local_datasource.dart

@@ -60,6 +60,48 @@ class FavoriteProductsLocalDataSource {
   bool isBoxOpen() {
     return Hive.isBoxOpen(HiveBoxNames.favoriteProductsBox);
   }
+
+  /// Check if a product is in favorites (local only - no API call)
+  bool isFavorite(String productId) {
+    try {
+      return _box.containsKey(productId);
+    } catch (e) {
+      _debugPrint('Error checking favorite: $e');
+      return false;
+    }
+  }
+
+  /// Get all favorite product IDs (local only - no API call)
+  Set<String> getFavoriteIds() {
+    try {
+      return _box.keys.cast<String>().toSet();
+    } catch (e) {
+      _debugPrint('Error getting favorite IDs: $e');
+      return {};
+    }
+  }
+
+  /// Add a product to local favorites cache
+  Future<void> addFavorite(ProductModel product) async {
+    try {
+      await _box.put(product.productId, product);
+      _debugPrint('Added to local favorites: ${product.productId}');
+    } catch (e) {
+      _debugPrint('Error adding to local favorites: $e');
+      rethrow;
+    }
+  }
+
+  /// Remove a product from local favorites cache
+  Future<void> removeFavorite(String productId) async {
+    try {
+      await _box.delete(productId);
+      _debugPrint('Removed from local favorites: $productId');
+    } catch (e) {
+      _debugPrint('Error removing from local favorites: $e');
+      rethrow;
+    }
+  }
 }
 
 /// Debug print helper