`prefs.theme` is dark, light or system, defaulting to dark: a reader
whose laptop is in light mode has said something about their laptop, not
about this page, and following the device would move every existing
reader the first time they loaded this. No control yet — the value can
only arrive from storage.
App resolves it and writes it to the document. It is also where a hue
meets the theme: doing that in the lane resolver means every label, chip,
rail and bar gets the readable answer without a component knowing a theme
exists, which is why the colophon moves onto that resolver too.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
