已完成用户APP首期功能开发

交付用户端首期页面、配套接口、后台资源及测试文档。用户APP构建、静态分析和三个管理后台构建通过；完整测试仍有2项失败，后端模型注释检查未通过，详见交付记录。

apps/user_app/lib/domain/models/cart_item.dart

@@ -0,0 +1,53 @@
+// 功能描述：购物车条目、并发版本和结算快照；版本：1.0.0。
+import 'primary_models.dart';
+
+/// 服务端购物车快照；revision 用于阻止过期操作覆盖其他设备的修改。
+class CartItem {
+  const CartItem({
+    required this.product,
+    required this.quantity,
+    required this.selected,
+    required this.available,
+    required this.revision,
+    this.specification = '',
+  });
+  final ProductSummary product;
+  final int quantity;
+  final bool selected, available;
+  final String revision;
+  final String specification;
+  bool get purchasable => available && quantity > 0 && quantity <= product.stock;
+  int get amount => product.price * quantity;
+
+  factory CartItem.fromJson(Map<String, Object?> json, String Function(String) resolve) {
+    final price = json['price_amount'], stock = json['stock_quantity'], quantity = json['quantity'];
+    if (price is! int ||
+        price < 0 ||
+        stock is! int ||
+        quantity is! int ||
+        quantity < 0 ||
+        quantity > 999 ||
+        json['product_identity'] is! String ||
+        (json['product_identity'] as String).isEmpty ||
+        json['revision'] is! String ||
+        json['selected'] is! bool ||
+        json['available'] is! bool) {
+      throw const FormatException('购物车数据异常');
+    }
+    return CartItem(
+      product: ProductSummary(
+        identity: json['product_identity'] as String,
+        name: json['name'] as String? ?? '',
+        price: price,
+        stock: stock,
+        imageUrl: resolve(json['image_url'] as String? ?? ''),
+        category: json['category_name'] as String? ?? '',
+      ),
+      quantity: quantity,
+      selected: json['selected'] as bool,
+      available: json['available'] as bool,
+      revision: json['revision'] as String,
+      specification: json['specification'] as String? ?? '',
+    );
+  }
+}