fix: Waffo webhook 支持 GET 探测，避免浏览器打开 404

仪表盘/浏览器用 GET 校验 URL 时返回 ready；支付事件仍走 POST。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/controller/order/order_controller.go

@@ -113,6 +113,16 @@ func (ctrl *OrderController) PaymentWebhook(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"code": 0, "message": "Webhook processed"})
 }
 
+// WaffoWebhookReady GET/HEAD probe for dashboard URL checks (browser opens as GET). // Logan.Li
+func (ctrl *OrderController) WaffoWebhookReady(c *gin.Context) {
+	c.JSON(http.StatusOK, gin.H{
+		"code":    0,
+		"message": "waffo webhook ready",
+		"methods": []string{"POST"},
+		"hint":    "Payment events must POST JSON with order_no / orderNo",
+	})
+}
+
 // WaffoWebhook accepts loosely-shaped Waffo payment events and maps to PaymentWebhook. // Logan.Li
 func (ctrl *OrderController) WaffoWebhook(c *gin.Context) {
 	body, err := io.ReadAll(c.Request.Body)