feat: 관리자 API(AdminController) 권한 검증 로직 추가

[seonghobae]

이 PR은 시스템 내 변환 작업 전체를 조회, 삭제, 재시도할 수 있는 관리자 API(AdminController)에 보안 권한 검증을 도입합니다.

추가 및 변경 사항

• TenantPermissions에 ADMIN_READ, ADMIN_WRITE 상수를 추가했습니다.
• AdminController의 모든 엔드포인트에 @RequestHeader HttpHeaders headers를 추가하고, TenantAccessService.require()를 호출하여 권한을 검증하도록 변경했습니다.
• 유닛 테스트(AdminControllerTest)에 TenantAccessService Mock을 추가하고 필수 헤더를 주입하도록 수정하여 기존 100% 테스트 커버리지를 유지했습니다.
• CHANGELOG.md에 추가된 내용을 업데이트했습니다.

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PR created automatically by Jules for task 14384608482565855960 started by @seonghobae

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