🛡️ Sentinel: 파일 교체 시 Atomic Move 적용을 통한 Race Condition 방지

[seonghobae]

보안 향상: 파일 교체 시 원자적 이동(Atomic Move)을 사용하여 Race Condition 방지

• write_index_file 함수에서 Files.move 시 StandardCopyOption.ATOMIC_MOVE 옵션을 사용하도록 수정
• AtomicMoveNotSupportedException 발생 시 기존 REPLACE_EXISTING으로 폴백 처리
• 100% 테스트 커버리지를 위한 fallback 테스트 코드 추가
• .jules/sentinel.md 에 학습 내용 기록

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PR created automatically by Jules for task 15862062086682834887 started by @seonghobae

[google-labs-jules]

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