Plan step 36. <x-group> renders data-md-group with its size, variant,
shape, multiple and inline, a data-md-button-group row and
data-md-group-segment labels over its radios or checkboxes. group.css
draws the segments as M3's buttons with the toggle button's colours
from :has(:checked), the disabled treatment from :has(:disabled), the
focus ring from :has(:focus-visible) and the 48px target at xs and sm.
The connected shapes move into button-group.css (the corner scale,
square ends, the pressed and selected inner corners), which group.css
imports; <x-button-group> adopts them in its own rewrite. The group's
render tests move to GroupTest; AppBarTest (navigation group) follows
the new legend and row hooks of theme-toggle's rows.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
