Move the documentation from Sphinx to Zensical, refresh the README and its animations - #500

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: technote-space/toc-generator@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/