MkDocs alternatives: preserve the documentation build and URLs

For MkDocs alternatives, build the same small documentation site from the existing Markdown source.

• Check navigation, search, code highlighting, admonitions, and plugin-dependent syntax.
• Compare build speed, accessibility, mobile layout, and offline reading if needed.
• Test versioned docs, localization, and deployment pipeline.
• Keep old URLs or add redirects; crawl the generated site for broken links.
• Rebuild on a clean machine with pinned dependencies.

A theme demo is not a migration test. The documentation must remain findable and reproducible from source.