feat: rebuild site with Astro

[rmax]

Summary

Rebuild the rmax.ai static site with Astro so shared UI is componentized and note pages are generated from Markdown.

Changes

• Add Astro source structure with shared layout, header, footer, note-card, and section-page components.
• Generate all published note routes and the notes index from the existing Markdown collection.
• Add static routes for the homepage, Apps, Projects, Research, Start Here, Token, New to AI FDE, and Slides.
• Preserve the custom-domain deployment contract through public CNAME and .nojekyll files.
• Add GitHub Pages deployment and sitemap generation.
• Correct non-semantic YAML formatting in four note frontmatters required for collection parsing.

Verification

• ASTRO_TELEMETRY_DISABLED=1 npm run check — 0 errors, warnings, or hints.
• ASTRO_TELEMETRY_DISABLED=1 npm run build — 66 static pages, sitemap, CNAME, and .nojekyll generated.

Risk / Rollback

The deployment model changes from serving committed root HTML to a GitHub Actions-built dist/ artifact. Reverting this commit restores the previous static-site source and deployment behavior.

Reviewer Notes

The existing uncommitted edit to new-to-ai-fde/index.html is intentionally excluded.

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