A landing page, and a documentation pass

SkillHub is in public beta and has a landing page to show for it. The documentation site got a pass alongside it.

Highlights

• A landing page. The root of the site shows what the product does: publishing a skill, installing it across an organization, versions, provenance, and who can change what. Signed-in visitors go to their dashboard instead.
• Look around without an account. Public owner profiles, registries and skill pages are readable signed out, inside the landing page's own navigation and footer.
• The documentation site matches the app. It uses the same fonts, palette and chrome.
• New documentation. A security page on archive safety covers what the registry checks in an uploaded skill tarball: path and symlink rules, the size limits that apply during decompression, and the rejection codes you can branch on. Troubleshooting adds three common skillhub publish failures with their exit codes.
• A health endpoint. /api/health reports whether the API host can reach its database, object store and auth adapter, and names the build that answered.