Add Supabase skills and harden Regélő app state - #1

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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, denoland/setup-deno@61fe2df320078202e33d7d5ad347e7dcfa0e8f31. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/