Native checkboxes render as a light box regardless of accent-color, so
they stood out against the dark theme. Restyle input[type=checkbox]
with appearance:none to mirror the kanrisha web UI: an outlined box
that becomes an indigo-tinted box with a light indigo tick when checked
(plus an indeterminate dash and focus ring).
Sizing is left to the existing w-4/h-4 classes so the hidden
toggle-switch input is untouched. Folded into 0002-webui-dark-theme.patch.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>