fix: 完善审批流程错误处理和调试日志

主要修改：
1. 添加完整的 try-catch 错误处理
2. 添加 Transaction 开始/成功日志
3. 添加保存前后的状态日志
4. 捕获并记录任何异常

测试验证：
- 审批流程正常执行
- 状态正确更新为 approved
- 跳过 notify 节点直接完成
- "我已审批"列表正确返回数据

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/service/BusinessTripService.php

@@ -684,8 +684,10 @@ class BusinessTripService
     {
         error_log("📝 approve() 开始: userId={$userId}, businessTripId={$businessTripId}, action={$action}");
 
-        return $this->db->transaction(function () use ($userId, $businessTripId, $action, $comment) {
-            $businessTrip = BusinessTrip::with(['itineraries', 'approvalOrder'])->findOrFail($businessTripId);
+        try {
+            $result = $this->db->transaction(function () use ($userId, $businessTripId, $action, $comment) {
+                error_log("🔄 Transaction 开始");
+                $businessTrip = BusinessTrip::with(['itineraries', 'approvalOrder'])->findOrFail($businessTripId);
 
             if (!$businessTrip->approval_order_id) {
                 throw new \Exception('未找到审批单');
@@ -824,14 +826,27 @@ class BusinessTripService
                 }
             }
 
+            error_log("💾 准备保存: order_status={$approvalOrder->status}, trip_status={$businessTrip->status}");
+
             $approvalOrder->save();
             $businessTrip->save();
 
+            error_log("✅ 保存完成: order_id={$approvalOrder->id}, trip_id={$businessTrip->id}");
+
             // 发送审批结果通知
             $this->sendApprovalResultNotification($businessTrip, $action, $comment);
 
+            error_log("✅ Transaction 成功，返回结果");
+
             return $businessTrip->fresh(['itineraries', 'approvalOrder']);
-        });
+            });
+
+            error_log("📝 approve() 完成: result_id=" . $result->id);
+            return $result;
+        } catch (\Exception $e) {
+            error_log("❌ approve() 异常: " . $e->getMessage() . " in " . $e->getFile() . ":" . $e->getLine());
+            throw $e;
+        }
     }
 
     /**