fix: 修复删除按钮绝对定位

- 删除按钮添加z-index确保在最上层
- 商品项添加padding-top给删除按钮留空间
- 移除商品信息的padding-right

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/views/user/Cart.vue

@@ -952,25 +952,27 @@ onMounted(() => {
     flex-direction: column !important;
     flex-wrap: nowrap !important;
     padding: 10px !important;
-    position: relative;
+    padding-top: 36px !important;
+    position: relative !important;
     gap: 8px;
   }
 
   /* 复选框 - 左上角 */
   .cart-item > .el-checkbox {
-    position: absolute;
-    top: 10px;
-    left: 10px;
+    position: absolute !important;
+    top: 10px !important;
+    left: 10px !important;
     width: 24px !important;
+    z-index: 10 !important;
   }
 
   /* 删除按钮 - 右上角 */
   .cart-item > .item-action {
-    position: absolute;
-    top: 10px;
-    right: 10px;
+    position: absolute !important;
+    top: 10px !important;
+    right: 10px !important;
     width: auto !important;
-    display: block !important;
+    z-index: 10 !important;
   }
 
   /* 商品信息行 */
@@ -979,7 +981,6 @@ onMounted(() => {
     flex-direction: row !important;
     width: 100% !important;
     padding-left: 28px !important;
-    padding-right: 40px !important;
     margin-bottom: 8px !important;
     cursor: pointer;
   }