feat(orderConfirm): 优化订单确认页面功能和样式

- 添加优惠券选择功能
- 增加商品数量选择
- 完善订单信息展示
- 优化支付流程
- 添加错误状态和加载状态处理
- 新增 OrderConfirmSkeleton 组件用于加载骨架屏

src/components/QuantitySelector.scss

@@ -0,0 +1,121 @@
+.quantity-selector {
+  display: flex;
+  flex-direction: column;
+  align-items: flex-start;
+  gap: 4px;
+
+  &__controls {
+    display: flex;
+    align-items: center;
+    border: 1px solid #e5e5e5;
+    border-radius: 4px;
+    overflow: hidden;
+    background: #fff;
+  }
+
+  &__btn {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    border: none;
+    background: #f8f8f8;
+    color: #666;
+    transition: all 0.2s ease;
+    
+    &:active {
+      background: #e5e5e5;
+    }
+
+    &--disabled {
+      background: #f5f5f5 !important;
+      color: #ccc !important;
+      cursor: not-allowed;
+    }
+  }
+
+  &__input {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    background: #fff;
+    border-left: 1px solid #e5e5e5;
+    border-right: 1px solid #e5e5e5;
+  }
+
+  &__value {
+    font-size: 14px;
+    color: #333;
+    font-weight: 500;
+    text-align: center;
+  }
+
+  &__stock {
+    margin-top: 2px;
+  }
+
+  &__stock-text {
+    font-size: 12px;
+    color: #999;
+  }
+
+  // 尺寸变体
+  &--small {
+    .quantity-selector__controls {
+      height: 24px;
+    }
+
+    .quantity-selector__btn {
+      width: 24px;
+      height: 24px;
+    }
+
+    .quantity-selector__input {
+      width: 32px;
+      height: 24px;
+    }
+
+    .quantity-selector__value {
+      font-size: 12px;
+    }
+  }
+
+  &--medium {
+    .quantity-selector__controls {
+      height: 32px;
+    }
+
+    .quantity-selector__btn {
+      width: 32px;
+      height: 32px;
+    }
+
+    .quantity-selector__input {
+      width: 40px;
+      height: 32px;
+    }
+
+    .quantity-selector__value {
+      font-size: 14px;
+    }
+  }
+
+  &--large {
+    .quantity-selector__controls {
+      height: 40px;
+    }
+
+    .quantity-selector__btn {
+      width: 40px;
+      height: 40px;
+    }
+
+    .quantity-selector__input {
+      width: 48px;
+      height: 40px;
+    }
+
+    .quantity-selector__value {
+      font-size: 16px;
+    }
+  }
+}