refactor: switch to verso blueprint - #89

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: leanprover-community/upstreaming-dashboard-action@main, ruby/setup-ruby@eaecf785f6a34567a6d97f686bbb7bccc1ac1e5c. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/