feat(tkuser): 알림 시스템 이관 system1-factory → tkuser

- Phase 1: tkuser에 알림 CRUD, Push/ntfy 발송, 내부 알림 API 추가
- Phase 2: notifyHelper URL을 tkuser-api:3000으로 전환 (system2, tkpurchase, tksafety, system1)
- Phase 3: notification-bell.js API 도메인 tkuser로 변경 + 캐시 버스팅 v=4
- Phase 4: system1에서 알림 코드 제거 (routes, controllers, models, utils)

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

tksupport/web/static/js/tksupport-core.js

@@ -164,7 +164,7 @@ function initAuth() {
 /* ===== 알림 벨 ===== */
 function _loadNotificationBell() {
     const s = document.createElement('script');
-    s.src = (location.hostname.includes('technicalkorea.net') ? 'https://tkds.technicalkorea.net' : location.protocol + '//' + location.hostname + ':30000') + '/shared/notification-bell.js?v=3';
+    s.src = (location.hostname.includes('technicalkorea.net') ? 'https://tkds.technicalkorea.net' : location.protocol + '//' + location.hostname + ':30000') + '/shared/notification-bell.js?v=4';
     document.head.appendChild(s);
 }