Allow docs to have versions (v1, v2, latest) for products with API/product versioning. Docs routes support /docs/v1/... and /docs/latest/... with canonical metadata. Admin can duplicate a docs version, mark one as default, and deprecate old versions.

Schema: doc_versions plus doc_pages.version_id. Migration keeps existing docs in a default latest version. Public UI gets version switcher. Useful later when docs content grows.