Add JSON-LD and llms.txt for AI search - #1006

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v3, actions/cache@v4, actions/checkout@v4, actions/setup-node@v4, actions/upload-artifact@v4, erlef/setup-beam@v1.20.4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/