Add role="separator" + aria-valuenow/min/max/orientation + tabIndex={0}
to make the resize handle focusable and discoverable by screen readers
(WAI-ARIA slider pattern). Add onKeyDown handler: ArrowLeft/Right moves
by 16px, Home/End snaps to min/max. Persist width to localStorage on
keyboard resize, matching the existing mouse behaviour.
Focus ring uses focus-visible:ring-2 to avoid showing on mouse click.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>