fix: 修复 BusinessTripService 中未定义变量 $node 的问题

- 将 $node 作为参数传递给 sendApprovalNotification() 方法
- 修复消息发送时 'Undefined variable $node' 错误

backend/app/service/BusinessTripService.php

@@ -269,7 +269,7 @@ class BusinessTripService
             // 发送飞书通知给审批人
             error_log("🔔 准备发送审批通知，调用 sendApprovalNotification 方法");
             error_log("📋 传递的参数 - approverIds: " . json_encode($approverIds) . ", ccUserIds: " . json_encode($ccUserIds));
-            $this->sendApprovalNotification($businessTrip, $approverIds, $ccUserIds);
+            $this->sendApprovalNotification($businessTrip, $approverIds, $ccUserIds, $node);
 
             return $businessTrip->fresh(['itineraries', 'approvalOrder']);
         });
@@ -278,7 +278,7 @@ class BusinessTripService
     /**
      * 发送审批通知（飞书消息）
      */
-    private function sendApprovalNotification(BusinessTrip $businessTrip, array $approverIds, array $ccUserIds): void
+    private function sendApprovalNotification(BusinessTrip $businessTrip, array $approverIds, array $ccUserIds, ApprovalNode $node): void
     {
         try {
             error_log("🔔 准备发送审批通知: trip_id={$businessTrip->id}, approvers=" . json_encode($approverIds) . ", cc=" . json_encode($ccUserIds));