chore(ci) : GCP_SA_KEY 제거 및 Docker 이미지 직접 전송 방식으로 배포 전환 - #159

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, actions/setup-java@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/