fix(purchase): 작업일정 삭제 시 관련 데이터 캐스케이드 삭제 (admin 전용)

- 삭제 권한을 admin 전용으로 변경 (requireAdmin)
- 트랜잭션으로 reports → checkins → safety_education → schedule 순서 삭제
- 프론트엔드: admin만 삭제 버튼 표시, 종속 데이터 삭제 경고 추가
- 404 처리 및 한국어 에러 메시지

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

tkpurchase/api/routes/scheduleRoutes.js

@@ -1,6 +1,6 @@
 const express = require('express');
 const router = express.Router();
-const { requireAuth, requirePage } = require('../middleware/auth');
+const { requireAuth, requireAdmin, requirePage } = require('../middleware/auth');
 const ctrl = require('../controllers/scheduleController');
 
 router.use(requireAuth);
@@ -14,6 +14,6 @@ router.put('/:id', requirePage('purchasing_schedule'), ctrl.update);
 router.put('/:id/status', requirePage('purchasing_schedule'), ctrl.updateStatus);
 router.put('/:id/approve', requirePage('purchasing_schedule'), ctrl.approveRequest);
 router.put('/:id/reject', requirePage('purchasing_schedule'), ctrl.rejectRequest);
-router.delete('/:id', requirePage('purchasing_schedule'), ctrl.deleteSchedule);
+router.delete('/:id', requireAdmin, ctrl.deleteSchedule);
 
 module.exports = router;