fix: [approvals] 결재선 저장 시 직책(job_title) fallback 추가

- enrichLineSteps: position_label → job_title_label fallback
- saveApprovalSteps: 동일 fallback 적용
- position_key가 NULL이고 job_title_key만 있는 사용자 대응

app/Services/ApprovalService.php

@@ -634,7 +634,7 @@ public function saveApprovalSteps(Approval $approval, array $steps): void
 
                 if ($employee) {
                     $departmentName = $employee->department?->name;
-                    $positionName = $employee->position_label;
+                    $positionName = $employee->position_label ?? $employee->job_title_label;
                 }
             }
 
@@ -707,7 +707,7 @@ private function enrichLineSteps(array $steps): array
                 'user_id' => $step['user_id'],
                 'user_name' => $user?->name ?? '',
                 'department' => $profile?->department?->name ?? $step['department'] ?? '',
-                'position' => $profile?->position_label ?? $step['position'] ?? '',
+                'position' => $profile?->position_label ?? $profile?->job_title_label ?? $step['position'] ?? '',
                 'step_type' => $step['step_type'] ?? 'approval',
             ];
         })->toArray();