[kattni]

Migrates Toga's documentation build from MkDocs to Zensical (0.1.0), using the Zensical support in beeware-docs-tools.

Depends on beeware/beeware-docs-tools#288. Until that merges, the docs dependency group pins beeware-docs-tools to the migration branch (kattni/beeware-docs-tools@tooling/zensical-migration), with a TEMPORARY comment. The pin will be reverted to beeware-docs-tools main once #288 merges, before this PR is merged.

Changes

• Configuration: docs/config.yml and docs/mkdocs.en.yml are converted to docs/zensical.toml and docs/zensical.en.toml with docs-tools' convert_mkdocs_config.
• Navigation: the literate-nav docs/en/SUMMARY.md is replaced by an explicit nav in zensical.toml. Its wildcard sections (tutorial/*, topics/* and the reference/api/* subsections) are expanded to explicit page lists.
• Snippets: the exclude plugin is replaced by core exclude_docs = "snippets/".
• Dependencies: mkdocs-redirects and mkdocs-exclude are dropped from the docs group; Zensical implements both natively. The redirects configuration is unchanged.
• tox: removes the MkDocs 2 warning environment variables and the --source-code arguments (docs-tools now resolves the mkdocstrings paths from the repo root).
• Housekeeping: .gitignore ignores the generated docs/_build.*.toml configs; the rumdl exclude no longer lists SUMMARY.md; AGENTS.md describes the Zensical setup.

Verification

• tox -e docs (strict) passes against docs-tools b3a1e03.
• The output was compared with a MkDocs build of main:
  • All 164 pages are present, and their titles match.
  • The sidebar navigation is identical.
  • All 44 redirects are byte-identical.
  • objects.inv is identical (3,499 entries), and so are the external cross-references to Python and Pillow.
  • There are no broken local links or images.
  • Article text matches on all but 7 pages:
    • 3 are cosmetic: equivalent image paths, and an HTML-escaped autorefs title.
    • 4 are contribution-guide pages whose shared docs-tools content was intentionally updated for the Zensical nav.
• Visually, the pages match the MkDocs build in light and dark mode. The only visible change is Zensical's compact search button.

Notes for reviewers

• Nav must now be maintained by hand. New pages have to be added to nav in docs/zensical.toml. Zensical 0.1.0 doesn't implement MkDocs' "page not in nav" (omitted_files) validation, so a page missing from nav builds silently rather than failing the strict build. Is that acceptable, or should we add a check?
• The docs-tools pin must be reverted before merge, once Migrate the documentation tooling to Zensical beeware-docs-tools#288 lands.
• rumdl keeps flavor = "mkdocs", because Zensical uses the same Markdown dialect.

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)