feat: AtchaV2 Phase 12 — 폴백·하드닝 (알림 권한 + dismiss 로컬 노티 + 실패·종료 상태) - #350

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/