feat: add public website and cross-agent skill install

[apresmoi]

Summary

• add an Astro + Starlight docs and landing site under website/ (its own package; the repo root stays zero-runtime-dep)
• style the site to the dashboard/ovens design system (black, monospace body, flat Helvetica headings, blue accent, the triangle mark)
• add burnlist install/burnlist uninstall — register the skill for both Claude Code (.claude/skills) and Codex (.agents/skills), per-repo or --global
• document the two independent installable systems on the site: skills via burnlist install, hooks via burnlist hooks install (install one, the other, or both)
• emit agent-ready build artifacts: llms.txt, llms-full.txt, per-page .md, sitemap, and a self-contained skill.md
• offer a two-path install — global npm, or hand an agent the skill.md URL — each with a copy button
• sync docs with main: add the Visual Parity Oven page and sidebar entry, and the Differential Testing scenario engine/contractSha256 field
• make the atomic-quarantine install identity survive Linux inode reuse by pairing {dev, ino} with mtimeMs

Validation

• npm run build:dashboard
• npm run verify — 486 tests passed
• npm run verify:package
• cd website && npm run build — site plus llms/sitemap/skill.md artifacts

Context

Combines the public-website and cross-agent skill-install work built off main; both merged onto the current tree conflict-free. Known follow-up (pre-existing, not introduced here): at narrow widths (<= 430px) some text clips at the right edge instead of wrapping, on Starlight docs pages and the landing alike.