`mode="picker"` hand-rolled an outlined segmented button, point for point the
design M3 Expressive deprecates, and its own arrow keys neither wrapped nor
handled Up/Down. Both rows are now <x-group>: native radios in a fieldset, so the
browser supplies the radiogroup, both axes, the wrap and the roving tab stop, and
the store is bound through an x-model accessor — a contrast row still marks the
resolved level but writes through setContrast(). A new `label` prop legends the
row. Plan: docs/plans/material-3-alignment.md, step 14 (navigation N-04, N-17).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
