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/schedule.html

@@ -211,8 +211,21 @@
         </div>
     </div>
 
-    <script src="/static/js/tkpurchase-core.js?v=20260312"></script>
-    <script src="/static/js/tkpurchase-schedule.js?v=20260312"></script>
+    <!-- 체크인 상세 모달 -->
+    <div id="checkinModal" class="hidden modal-overlay" onclick="if(event.target===this)closeCheckinModal()">
+        <div class="modal-content p-6" style="max-width:600px">
+            <div class="flex justify-between items-center mb-4">
+                <h3 class="text-lg font-semibold">체크인 현황</h3>
+                <button onclick="closeCheckinModal()" class="text-gray-400 hover:text-gray-600"><i class="fas fa-times"></i></button>
+            </div>
+            <div id="checkinModalBody" class="space-y-3">
+                <p class="text-gray-400 text-center py-4">로딩 중...</p>
+            </div>
+        </div>
+    </div>
+
+    <script src="/static/js/tkpurchase-core.js?v=20260313"></script>
+    <script src="/static/js/tkpurchase-schedule.js?v=20260313"></script>
     <script>initSchedulePage();</script>
 </body>
 </html>