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.tsx

@@ -0,0 +1,88 @@
+import React from 'react'
+import { View, Text } from '@tarojs/components'
+import { Button } from '@nutui/nutui-react-taro'
+import { Minus, Plus } from '@nutui/icons-react-taro'
+import './QuantitySelector.scss'
+
+export interface QuantitySelectorProps {
+  /** 当前数量 */
+  value: number
+  /** 最小数量 */
+  min?: number
+  /** 最大数量（库存） */
+  max?: number
+  /** 是否禁用 */
+  disabled?: boolean
+  /** 数量变化回调 */
+  onChange?: (value: number) => void
+  /** 尺寸 */
+  size?: 'small' | 'medium' | 'large'
+  /** 是否显示库存提示 */
+  showStock?: boolean
+  /** 库存数量 */
+  stock?: number
+}
+
+const QuantitySelector: React.FC<QuantitySelectorProps> = ({
+  value,
+  min = 1,
+  max = 999,
+  disabled = false,
+  onChange,
+  size = 'medium',
+  showStock = false,
+  stock
+}) => {
+  const handleDecrease = () => {
+    if (disabled || value <= min) return
+    const newValue = value - 1
+    onChange?.(newValue)
+  }
+
+  const handleIncrease = () => {
+    if (disabled || value >= max) return
+    const newValue = value + 1
+    onChange?.(newValue)
+  }
+
+  const canDecrease = !disabled && value > min
+  const canIncrease = !disabled && value < max
+
+  return (
+    <View className={`quantity-selector quantity-selector--${size}`}>
+      <View className="quantity-selector__controls">
+        <Button
+          className={`quantity-selector__btn quantity-selector__btn--minus ${!canDecrease ? 'quantity-selector__btn--disabled' : ''}`}
+          size="small"
+          onClick={handleDecrease}
+          disabled={!canDecrease}
+        >
+          <Minus size={size === 'small' ? 12 : size === 'large' ? 16 : 14} />
+        </Button>
+        
+        <View className="quantity-selector__input">
+          <Text className="quantity-selector__value">{value}</Text>
+        </View>
+        
+        <Button
+          className={`quantity-selector__btn quantity-selector__btn--plus ${!canIncrease ? 'quantity-selector__btn--disabled' : ''}`}
+          size="small"
+          onClick={handleIncrease}
+          disabled={!canIncrease}
+        >
+          <Plus size={size === 'small' ? 12 : size === 'large' ? 16 : 14} />
+        </Button>
+      </View>
+      
+      {showStock && stock !== undefined && (
+        <View className="quantity-selector__stock">
+          <Text className="quantity-selector__stock-text">
+            库存 {stock} 件
+          </Text>
+        </View>
+      )}
+    </View>
+  )
+}
+
+export default QuantitySelector