fix(backend): 购物车项单价有SKU时用规格价，修复购物车显示商品价而非规格价

cfc-backend/src/main/java/com/etotem/cfc/service/CartService.java

@@ -151,7 +151,11 @@ public class CartService {
         }
         if (cart.getSkuId() != null) {
             ProductSku sku = productSkuService.getById(cart.getSkuId());
-            if (sku != null && sku.getSpecs() != null) {
+            if (sku != null) {
+                if (sku.getPrice() != null) {
+                    dto.setUnitPrice(sku.getPrice());
+                }
+                if (sku.getSpecs() != null) {
                 try {
                     String specsStr = sku.getSpecs().toString().trim();
                     StringBuilder specDesc = new StringBuilder();
@@ -183,6 +187,7 @@ public class CartService {
                 } catch (Exception e) {
                     log.warn("解析SKU specs失败: skuId={}", cart.getSkuId(), e);
                 }
+                }
             }
         }
         return dto;