Temp fix decade-long Sphinx bug breaking our CSS during partial rebuilds

[pushfoo]

TL;DR: Ship 3.0 by letting you edit CSS without ./make.py clean 😱!

How do I use this & When?

Does CSS not copy right on your local machine? Then:

1. cd $ARCADE_DIR
2. touch .ENABLE_DEVMACHINE_SPHINX_STATIC_FIX
3. ./make.py html or ./make.py serveas usual

Why do this?

TL;DR: Debugging CSS is already hard enough

1. Sphinx's _static has been making CSS harder by being broken since at least 2015
2. This fixes it for both:
   • ./make.py html
   • ./make.py serve (it's based on sphinx-autobuild, see this comment for more).

Technical Details

1. Sphinx rebuilds haven't copied updated CSS correctly since at least 2015 (Files from _static are not copied automatically sphinx-doc/sphinx#1810)
2. The solutions have traditionally been:
   • The equivalent of our ./make.py clean (slow, hurts)
   • Write your own awful kludge
3. There's a fix in the works upstream, but...
   • It's been broken since 2015
   • The PR got merged Unconditionally copy static assets in Builder sphinx-doc/sphinx#13236 on Jan 15th, 2025
   • It's slated for release in 8.2.0
   • Sphinx 8.2.0 may break:
     • our theme
     • plugins
     • customization kludges
     • etc

Does this affect CI runs / readthedocs / code quality scans?

No.