feat: add Google sign-in and FCM push for the Android client - #6

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683, astral-sh/setup-uv@e92bafb6253dcd438e0484186d7669ea7a8ca1cc. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/