Plugins declare site-root path claims (exact or prefix) and a sitemap
contribution flag in plugin.mod; the packer validates and stamps them
into PluginManifest. Validation rejects reserved prefixes (/admin,
/api/plugins, /ws), traversal, duplicates, and prefix claims that cover
a reserved prefix.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
