Landing expansion and SEO plumbing

The marketing site grew up. We added FAQ, a three-step how-it-works, four use cases, and an inline live changelog so visitors see the product working without signing up.

Standalone pages went live: /docs with a sticky table of contents, /about in short editorial form, and /roadmap with shipping, considering, and done columns.

SEO plumbing wired up too: generated Open Graph and Twitter images, a Supabase-backed sitemap.xml, and a clean robots.txt. The navbar now surfaces docs, roadmap and about so nothing is buried in the footer.