Two-part solution for automatic CSS updates during development:
1. `bb watch-theme` — polls src/ui/*.css and tokens.edn every 500ms,
rebuilds dist/theme.css and copies to dev targets on change.
2. `dev/css-live-reload.js` — browser-side script that polls /theme.css
and hot-swaps the stylesheet without a full page reload (no FOUC).
The watcher runs automatically in the hiccup tmux pane when using
`bb dev-all`. It can also be run standalone with `bb watch-theme`.
The live-reload script is included in all three dev targets (hiccup,
replicant, squint) and copied by `bb build-theme`.
