Add landing page + Starlight docs site (#375)

* udpated matrix

* feat(site): add landing page + Starlight docs site

Astro + Starlight site in site/ — a flat/paper editorial landing page
plus 18 docs pages seeded from the README. Monochrome theme, hairline
rules, square corners, live GitHub star count, light default + dark
toggle. Deploys to GitHub Pages via .github/workflows/deploy-site.yml.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>