Documentation audit

DocKit’s existing check command validates configuration and builds a site, but a successful build can still contain a public link to an unpublished page, a missing fragment or an inaccessible image.

The audit command therefore builds a read-only model from configured public pages, their real source references and renderer heading IDs. It reports only probable publication mistakes. In particular, unlisted Markdown stays quiet unless a published page links to it, and external URLs are not network-checked.

This keeps the command deterministic and useful in offline CI while preserving the established separation: check is build correctness; audit is publication-readiness diagnostics.