seo: fix duplicate tags, add structured data and sitemap/robots coverage - #89

Process completed with exit code 1.

Could not fetch an OIDC token. Make sure to add `id-token: write` to your workflow permissions.

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