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>

---------

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

site/src/content.config.ts

@@ -0,0 +1,7 @@
+import { defineCollection } from 'astro:content';
+import { docsLoader } from '@astrojs/starlight/loaders';
+import { docsSchema } from '@astrojs/starlight/schema';
+
+export const collections = {
+	docs: defineCollection({ loader: docsLoader(), schema: docsSchema() }),
+};