웨이트테이블 백업 구현(백엔드)

[yjeong-k]

PR Title: 웨이트 테이블 백업 백엔드 구현

Related Issue(s):

PR Description:

• settings에 updated_at 필드 추가 (DB에도)
• GET setting/backup/의 response에 상기 updated_at 포함되도록 변경
• 웨이트테이블 백업 API 구현
• Wiki API specification, DB schema, Backend class diagram 수정

Changes Included:

• Added new feature(s)
• Fixed identified bug(s)
• Updated relevant documentation

Notes for Reviewer:

Reviewer Checklist:

• Code is written in clean, maintainable, and idiomatic form.
• Automated test coverage is adequate.
• All existing tests pass.
• Manual testing has been performed to ensure the PR works as expected.
• Code review comments have been addressed or clarified.

Additional Comments: