[REFACTOR] 인증 영역의 잔존 코드와 주입 컨벤션 정리 - #188

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v3, actions/checkout@v4, actions/setup-java@v4, gradle/gradle-build-action@v2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Failed to restore v8-gradle|Linux|backend-ci.yml-test[37a6259cc0c1dae299a7866489dff0bd]-9dba98993f5d9a06158b87fb95e980deb0ef5d66: Error: Cache service responded with 400