feat: add docs + blog pages, consolidate doc surfaces

- Add docs.html: card-based documentation hub linking to all guides
- Add blog.html: research blog (migrated from corvid-pages repo)
- Update index.html nav: add Docs + Blog links, remove Business Guide link

Consolidates 4 doc surfaces (README, /docs, .github.io, corvid-pages)
into 2: a slim README + one unified website.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: corvid-agent