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/router/router.go

@@ -109,6 +109,7 @@ func SetupRouter(db *gorm.DB, cfg *config.Config) *gin.Engine {
 			register(clientAPI, "POST", "/checkout", orderController.Checkout)
 			register(clientAPI, "POST", "/purchase/claim", orderController.ClaimPurchase)
 			register(clientAPI, "POST", "/webhooks/payment", orderController.PaymentWebhook)
+			register(clientAPI, "GET", "/webhooks/waffo", orderController.WaffoWebhookReady)
 			register(clientAPI, "POST", "/webhooks/waffo", orderController.WaffoWebhook)
 			register(clientAPI, "POST", "/purchase/check", orderController.CheckDuplicatePurchase)
 			register(clientAPI, "POST", "/purchase/status", orderController.CheckPurchaseStatus)