[kattni]

Moves Rubicon's documentation build from MkDocs and Material for MkDocs to Zensical, as part of the BeeWare-wide docs migration. The configuration now uses Zensical's native TOML format instead of MkDocs YAML.

This depends on beeware/beeware-docs-tools#288, which moves the shared docs tooling to Zensical. Until that PR merges, the docs dependency group is temporarily pinned to its branch (kattni/beeware-docs-tools@tooling/zensical-migration), so this PR builds. The pin is reverted to beeware/main once beeware/beeware-docs-tools#288 is merged.

Changes

• Configuration: docs/config.yml is now docs/zensical.toml, and docs/mkdocs.en.yml is now docs/zensical.en.toml. Both were generated by docs-tools' convert_mkdocs_config, which checked that the TOML configuration is equivalent to what Zensical read from the YAML.
• Navigation: the literate-nav file docs/en/SUMMARY.md is replaced by the native nav setting in docs/zensical.toml, and the literate-nav plugin is removed.
• tox: removed the DISABLE_MKDOCS_2_WARNING / NO_MKDOCS_2_WARNING environment variables, and the --source-code=stubs arguments; docs-tools now resolves the mkdocstrings paths (src, stubs) from the repository root.
• .gitignore: ignores docs/_build.*.toml, the per-language configuration docs-tools writes during a build.
• AGENTS.md: describes the docs as built with Zensical.
• Temporary pin: beeware-docs-tools in the docs dependency group, as described above.

There are no content changes to the documentation itself.

Verification

• tox -r -e docs (installing docs-tools at b3a1e03 from the pinned branch) builds in strict mode with no issues. tox -e docs-lint and tox -e pre-commit pass.
• Compared with a MkDocs build of main:
  • Article text is identical on 47 of 51 pages. The other 4 are shared contribution-guide pages, where docs-tools now describes nav instead of SUMMARY.md.
  • Navigation: the sidebar, tabs and previous/next links match on all 51 pages.
  • API reference: the pages built from src and stubs are identical, including members that only exist in the stubs (so find_stubs_package is honoured). objects.inv is identical (234 entries), and links to the Python docs via inventories resolve the same.
• Strict mode fails on a missing page, a missing anchor, an unresolved cross-reference and a bad ::: identifier, so the existing validation settings still apply.

Notes for reviewers

• Visual differences: these are Zensical theme differences, with docs-tools' default classic variant in use: a compact search box, slightly different inline code styling, and the sidebar no longer repeating the current page's headings.
• site_url: the converter moved the literal site_url into zensical.toml. As before, it takes precedence over the canonical URL from Read the Docs.
• Not changed here (existing behaviour): the pymdownx.magiclink settings use repo = "toga". As a result, #40 in the release notes links to a Toga issue, and @property in topics/memory-management.md is rendered as a GitHub user link. This should probably be rubicon-objc; I've left it for a separate change.
• Translations: Rubicon isn't translated, but in a test with a synthetic locale, po2md collapses the indented options: blocks under ::: directives, and the translated build fails. This happens under both MkDocs and Zensical, so it isn't a regression.
• Stale reference: .specify/memory/constitution.md still says the docs are built with Sphinx. It's only meant to change through the SpecKit constitution workflow, so I didn't edit it.

PR Checklist:

• I will abide by the BeeWare Code of Conduct
• I have read and have followed the CONTRIBUTING.md file
• This PR was generated or assisted using an AI tool

Assisted-by: Claude Code (Claude Opus 5.5)