feat: add admin order refund flow

Co-authored-by: multica-agent <github@multica.ai>

apis/admin/order.api

@@ -33,6 +33,10 @@ type (
 		PaymentId int64  `json:"payment_id,omitempty"`
 		TradeNo   string `json:"trade_no,omitempty"`
 	}
+	RefundOrderRequest {
+		Id     int64  `json:"id" validate:"required"`
+		Reason string `json:"reason,omitempty" validate:"omitempty,max=500"`
+	}
 	ActivateOrderRequest {
 		OrderNo string `json:"order_no" validate:"required"`
 	}
@@ -68,6 +72,10 @@ service ppanel {
 	@handler UpdateOrderStatus
 	put /status (UpdateOrderStatusRequest)
 
+	@doc "Refund order"
+	@handler RefundOrder
+	post /refund (RefundOrderRequest)
+
 	@doc "Manually activate order"
 	@handler ActivateOrder
 	post /activate (ActivateOrderRequest)