feat(tkpurchase): 체크인 worker_names 배열 저장 + 구매팀 체크인 관리 기능

- doCheckIn()에서 worker_names를 콤마 split 배열로 전송 (DB에 JSON 배열로 저장)
- 구매팀 일정 페이지에 체크인 조회/수정/삭제 모달 추가
- DELETE /checkins/:id endpoint + 트랜잭션 삭제 (reports cascade)
- PUT /checkins/:id에 requirePage 권한 guard 추가

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

tkpurchase/web/static/js/tkpurchase-partner-portal.js

@@ -421,12 +421,15 @@ async function openEditReport(reportId, checkinId, scheduleId) {
 
 async function doCheckIn(scheduleId) {
     const workerCount = parseInt(document.getElementById('checkinWorkers_' + scheduleId).value) || 1;
-    const workerNames = document.getElementById('checkinNames_' + scheduleId).value.trim();
+    const rawNames = document.getElementById('checkinNames_' + scheduleId).value.trim();
+    const workerNames = rawNames
+        ? rawNames.split(/[,，]\s*/).map(n => n.trim()).filter(Boolean)
+        : null;
 
     const body = {
         schedule_id: scheduleId,
         actual_worker_count: workerCount,
-        worker_names: workerNames || null
+        worker_names: workerNames
     };
 
     try {