feat: AtchaV2 Phase 4 — DesignSystem 신규 구축 (TDS식 2계층 토큰 + 컴포넌트 11종 + 갤러리) - #342

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/