fix(shop-cart): 修复购物车后端查询及前后端字段名对齐问题

- 修复后端ShopCartMapper SQL，关联查询商品和SKU信息，返回完整商品详情字段
- 新增ShopCart实体非持久化字段，映射商品名称、图片、价格、库存等
- 调整后端Controller列表方法，自动过滤当前登录用户购物车数据
- 前端ShopCart接口新增salePrice、dealerPrice字段，CartContext映射新增字段
- 修正购物车数量和选中状态字段名，前端与后端统一使用cartNum和selected
- 统一更新购物车数量、选中状态的接口调用参数，避免因字段不匹配导致更新失败
- 购物车及结算页价格显示逻辑优先使用后端扁平dealerPrice字段，兼容VIP价格显示
- 各购物车相关页面调整添加购物车参数，确保字段名一致和正确传递

src/pages/shop/cart.tsx

@@ -182,7 +182,7 @@ const CartPage: React.FC = () => {
                     )}
                     <View className="flex justify-between items-center">
                       <Text className="text-sm font-bold text-red-500">
-                        ¥{isVipMember() && (item.product as any)?.dealerPrice ? (item.product as any).dealerPrice : (item.skuPrice || item.sku?.price || item.product?.salePrice || item.product?.price || '0')}
+                        ¥{isVipMember() && (item.dealerPrice || (item.product as any)?.dealerPrice) ? (item.dealerPrice || (item.product as any).dealerPrice) : (item.skuPrice || item.sku?.price || item.salePrice || item.product?.salePrice || item.product?.price || '0')}
                       </Text>
                       <View className="flex items-center gap-3">
                         <View className="w-6 h-6 rounded bg-gray-100 flex items-center justify-center" onClick={() => updateQuantity(item.goodsId, item.skuId, item.quantity - 1)}>

src/pages/shop/category.tsx

@@ -135,7 +135,7 @@ const CategoryPage: React.FC = () => {
     if (!requireLogin({ action: 'addToCart' })) return
     addToCart({
       goodsId: product.goodsId!,
-      num: product.step || 1,
+      cartNum: product.step || 1,
     }).then(() => {
       Taro.showToast({ title: '已加入购物车', icon: 'success' })
     }).catch(err => {

src/pages/shop/checkout.tsx

@@ -149,9 +149,9 @@ const CheckoutPage: React.FC = () => {
     if (!items || items.length === 0) return 0
     const vip = isVipMember()
     return items.reduce((sum, item) => {
-      // VIP 会员优先使用 dealerPrice
-      const dealerPrice = vip ? (item.product as any)?.dealerPrice : null
-      const unitPrice = dealerPrice || item.skuPrice || item.sku?.price || item.product?.salePrice || item.product?.price || 0
+      // VIP 会员优先使用 dealerPrice（后端关联字段 > product 嵌套对象）
+      const dealerPrice = vip ? (item.dealerPrice || (item.product as any)?.dealerPrice) : null
+      const unitPrice = dealerPrice || item.skuPrice || item.sku?.price || item.salePrice || item.product?.salePrice || item.product?.price || 0
       return sum + Number(unitPrice) * (item.quantity || item.num || 1)
     }, 0)
   }, [buyNowItems, selectedItems])
@@ -368,7 +368,7 @@ const CheckoutPage: React.FC = () => {
                       <View className='flex justify-between items-center mt-1'>
                         <Text className='text-xs text-gray-500'>x{item.quantity || item.num || 1}</Text>
                         <Text className='text-sm font-medium text-gray-800'>
-                          ¥{isVipMember() && (item.product as any)?.dealerPrice ? (item.product as any).dealerPrice : (item.skuPrice || item.sku?.salePrice || item.sku?.price || item.product?.salePrice || item.product?.price || '0')}
+                          ¥{isVipMember() && (item.dealerPrice || (item.product as any)?.dealerPrice) ? (item.dealerPrice || (item.product as any).dealerPrice) : (item.skuPrice || item.sku?.salePrice || item.sku?.price || item.salePrice || item.product?.salePrice || item.product?.price || '0')}
                         </Text>
                       </View>
                     </View>

src/pages/shop/index.tsx

@@ -147,7 +147,7 @@ const ShopPage: React.FC = () => {
     if (!requireLogin({ action: 'addToCart' })) return
     addToCart({
       goodsId: product.goodsId!,
-      num: product.step || 1,
+      cartNum: product.step || 1,
     }).then(() => {
       Taro.showToast({ title: '已加入购物车', icon: 'success' })
     }).catch(err => {