feat(user-auth-api): 依 auth.md 實作使用者登入（email＋密碼，BCrypt）、角色（VIEWER／EDITOR／ADMIN）、CSRF、登入限速與 /users 管理 API，取代 v0.1.0 的共用客服帳密 - #104

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

setup-java v4 is deprecated and will no longer receive updates. Please migrate to actions/setup-java@v5.