Switch to make singlehtml + Chromium for PDF output

[legoktm]

Instead of going through LaTeX, which has some limitations (e.g. can't use newer emojis), we can use sphinx's pre-existing "singlehtml" target, and just have a browser print it to PDF. Chromium has a better CLI setup for this, but in the future we can swap to Firefox if desired.

I think for the most part this will be a nicer experience for users, because it'll be much closer to what's already online (some CSS is different), and because it's just HTML, there'll be far less less gotchas of things that work in HTML mode but not in PDF mode.

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This was done by Claude after I got nerdsniped by @jskinne3.

Test plan

• Compare with existing PDF output, decide which is better.

Checklist

This change accounts for:

• local preview of changes beyond typo-level edits

[almet]

I've been using https://weasyprint.org/ to turn HTML documents into PDF (as a python library but it can be used as a CLI as well) with great results 🙂.

It requires to configure a bit more the CSS "print" target, but the upside is that you can have documents that have a nice paper feeling, disable some menus and information that don't make sense for print, but are are displayed in the HTML rendered for browsers.

It seems that there exists an integration for sphinx: https://pypi.org/project/sphinx-weasyprint-builder. I haven't tried it, but if you're willing to spend some time tweaking the CSS, I bet you won't regret it (plus, it doesn't need an actual browser)