docs: update docs to zensical

[srivarra]

Migrate docs from Sphinx + sphinx-polyversion to Zensical.

Why?

sphinx-polyversion has been a bit of a burden; from the fork dependency for setuptools_scm compatibility, uv run silently reverting the fork (#373), manual poly.py updates per release, and silent build failures deploying empty sites.

What changed

• RST docs converted to Markdown with mkdocstrings for API autodoc
• conf.py + poly.py replaced by zensical.toml
• CI simplified to build + deploy-pages with uv + zensical build
• Making use of the iohub logo!
• Updated CONTRIBUTING.md with new docs workflow

Tradeoffs

• No multi-version docs for now, Zensical versioning is on their roadmap but not yet shipped. I think this tradeoff is worthwhile as the docs are also easier to write, maintain, style and extend if it's just markdown files.

The docs still get deployed to GitHub Pages which doesn't allow for previewing them in CI. We are getting readthedocs access though (it's coming... eventually).

[talonchandler]

This is great @srivarra! Thank you for doing this.

• I rendered the docs locally, and they look good. No major issues.

• I'm not personally concerned about the lack of multiversioning. If it comes in the future that's great, but not necessary.

• Will the docs website show the docs from the latest release or the main branch? I'm fine with either, as long as the version that is shown on the top right of the docs page matches.

• Minor nits/improvements:

• This looks like a bug, but it's actually real in the docs. Maybe it can be rendered more cleanly? No need to spend a bunch of time on it:

- in CLI Reference I see a few minor double indents:

[talonchandler]

Minor changes requested. LGTM after those.

[srivarra]

@talonchandler

Will the docs website show the docs from the latest release or the main branch? I'm fine with either, as long as the version that is shown on the top right of the docs page matches.

It'll show whatever is on the main branch.