feat: 实现站内USDT收银台支付流程

- 后端: payment.go 支付处理(创建订单/回调通知/状态查询/签名算法)
- 后端: 新增公开支付通道API(PublicList,不暴露config)
- 前端: Checkout.vue 收银台页面(倒计时/二维码/支付轮询)
- 前端: Cart.vue 对接动态支付通道,选择bepusdt跳转收银台
- 前端: API添加paymentChannelApi和orderApi支付方法
- 路由: 注册checkout路由和支付相关API

backend/internal/api/handlers/payment_channel.go

@@ -16,6 +16,40 @@ func NewPaymentChannelHandler() *PaymentChannelHandler {
 	return &PaymentChannelHandler{}
 }
 
+func (h *PaymentChannelHandler) PublicList(c *gin.Context) {
+	var channels []models.PaymentChannel
+	utils.DB.Where("is_enabled = ?", true).Order("sort_order ASC, id ASC").Find(&channels)
+
+	type publicChannel struct {
+		ID        uint    `json:"id"`
+		Name      string  `json:"name"`
+		Code      string  `json:"code"`
+		Type      string  `json:"type"`
+		Icon      string  `json:"icon"`
+		FeeRate   float64 `json:"fee_rate"`
+		MinAmount float64 `json:"min_amount"`
+		MaxAmount float64 `json:"max_amount"`
+		SortOrder int     `json:"sort_order"`
+	}
+
+	var result []publicChannel
+	for _, ch := range channels {
+		result = append(result, publicChannel{
+			ID:        ch.ID,
+			Name:      ch.Name,
+			Code:      ch.Code,
+			Type:      ch.Type,
+			Icon:      ch.Icon,
+			FeeRate:   ch.FeeRate,
+			MinAmount: ch.MinAmount,
+			MaxAmount: ch.MaxAmount,
+			SortOrder: ch.SortOrder,
+		})
+	}
+
+	c.JSON(http.StatusOK, gin.H{"data": result})
+}
+
 func (h *PaymentChannelHandler) List(c *gin.Context) {
 	var channels []models.PaymentChannel
 	utils.DB.Order("sort_order ASC, id ASC").Find(&channels)