chore(website): upgrade to Astro 7, Starlight 0.42 and @astrojs/cloudflare 14

[anurag629]

Fixes the open Astro security alerts on the docs site, including the critical image optimization RCE (fixed in 7.2.8). Replaces #82, which didn't build. Website only, no package changes.

• astro 7.3.5, @astrojs/starlight 0.42.5, @astrojs/cloudflare 14.3.3, @astrojs/react 7, @astrojs/sitemap 3.7.4, tailwindcss 4.3.3, wrangler ^4.146 (needed by the adapter)
• wrangler.jsonc main now points at @astrojs/cloudflare/entrypoints/server. The build writes dist/server/wrangler.json with the same routes, observability and assets settings.
• imageService: 'compile' keeps build-time image handling. The v14 default would switch to the Cloudflare Images binding.
• Starlight's Markdown pipeline (satteri) resolves to its wasm build inside the Worker bundle, so the root package.json tells pnpm to also install wasm32 builds, and the docs prerender in Node (prerenderEnvironment: 'node') like the old adapter did.
• compressHTML: true keeps the HTML output the same, and session: false stops the adapter from adding a SESSION KV namespace.

Checked on Node 22 with pnpm 9.15: frozen install, pnpm -r build, typecheck and 156 tests pass. Ran the built Worker with wrangler dev: all 19 docs pages and the 404 are there (matches the live sitemap), status codes match production, /api/chat streams and answers the CORS preflight, and getSecret still reads Worker secrets (checked /api/visitors against a local stand-in for Upstash). Landing page and docs look the same as production, with no console errors. Worker bundle is about 660 KB gzipped.