refactor: 미사용 의존성 제거 + deprecated API 수정 + 정리

- SSO/System2: 미사용 redis, bcrypt, multer 의존성 제거
- System2: dbPool.js shim 삭제, workIssueModel을 config/database 직접 참조로 변경
- System3: deprecated datetime.utcnow() → datetime.now(timezone.utc)
- System3: deprecated @app.on_event("startup") → lifespan 패턴
- System3: 중복 /users 라우트 제거, 불필요 파일 삭제
- health-check.sh: tkuser API/Web 체크 추가
- tkuser nginx: upstream 이름 수정 (tk-system2-api → system2-api)

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

scripts/health-check.sh

@@ -46,6 +46,8 @@ check_service "System 2 API"        "http://localhost:30105/api/health"    30105
 check_service "System 2 Web"        "http://localhost:30180/"              30180
 check_service "System 3 API"        "http://localhost:30200/api/health"    30200
 check_service "System 3 Web"        "http://localhost:30280/"              30280
+check_service "tkuser API"          "http://localhost:30300/api/health"    30300
+check_service "tkuser Web"          "http://localhost:30380/"              30380
 check_service "phpMyAdmin"          "http://localhost:30880/"              30880
 
 echo ""