add firebase, add screen flow

lib/features/cart/data/repositories/cart_repository_impl.dart

@@ -32,7 +32,7 @@ class CartRepositoryImpl implements CartRepository {
   final CartLocalDataSource _localDataSource;
 
   @override
-  Future<List<CartItem>> addToCart({
+  Future<bool> addToCart({
     required List<String> itemIds,
     required List<double> quantities,
     required List<double> prices,
@@ -57,17 +57,24 @@ class CartRepositoryImpl implements CartRepository {
 
       // Try API first
       try {
-        final cartItemModels = await _remoteDataSource.addToCart(items: items);
+        final success = await _remoteDataSource.addToCart(items: items);
 
-        // Sync to local storage
-        await _localDataSource.saveCartItems(cartItemModels);
+        // Also save to local storage for offline access
+        if (success) {
+          for (int i = 0; i < itemIds.length; i++) {
+            final cartItemModel = _createCartItemModel(
+              productId: itemIds[i],
+              quantity: quantities[i],
+              unitPrice: prices[i],
+            );
+            await _localDataSource.addCartItem(cartItemModel);
+          }
+        }
 
-        // Convert to domain entities
-        return cartItemModels.map(_modelToEntity).toList();
+        return success;
       } on NetworkException catch (e) {
         // If no internet, add to local cart only
         if (e is NoInternetException || e is TimeoutException) {
-          // Add items to local cart
           for (int i = 0; i < itemIds.length; i++) {
             final cartItemModel = _createCartItemModel(
               productId: itemIds[i],
@@ -79,9 +86,7 @@ class CartRepositoryImpl implements CartRepository {
 
           // TODO: Queue for sync when online
 
-          // Return local cart items
-          final localItems = await _localDataSource.getCartItems();
-          return localItems.map(_modelToEntity).toList();
+          return true;
         }
         rethrow;
       }
@@ -167,7 +172,7 @@ class CartRepositoryImpl implements CartRepository {
   }
 
   @override
-  Future<List<CartItem>> updateQuantity({
+  Future<bool> updateQuantity({
     required String itemId,
     required double quantity,
     required double price,