[Work 62] 약속 Repository를 문서 단위로 재편하고 약속 날짜를 필수값으로 바꿨습니다. - #34

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/