feat(www): rebuild site with Astro

[thdxr]

Summary

• replace Blume with a standard Astro website and fully owned frontend
• keep the docs implementation self-contained under src/docs and preserve all authored MDX content
• add Pagefind search, base-aware links, code titles, link validation, and native Astro client navigation without animation
• preserve the installer proxy and raw OpenAPI document while adding a real website homepage

Verification

• bun typecheck in packages/www
• bun run check:generated in packages/www
• bun run build in packages/www
• full pre-push monorepo typecheck (32/32 packages)
• browser-verified homepage, docs navigation, OpenTUI fonts, responsive layout, and Pagefind search

Note

The previous generated per-operation API UI is replaced by a lightweight /docs/api overview linking the raw OpenAPI specification.