fix: BepUsdt签名amount改用fmt.Sprint与请求体float64序列化一致

backend/internal/api/handlers/payment.go

@@ -78,7 +78,7 @@ func (h *PaymentHandler) CreatePayment(c *gin.Context) {
 
 	params := map[string]string{
 		"order_id":     strconv.Itoa(int(order.ID)),
-		"amount":       fmt.Sprintf("%.2f", order.TotalAmount),
+		"amount":       fmt.Sprint(order.TotalAmount),
 		"notify_url":   notifyURL,
 		"redirect_url": redirectURL,
 	}