QbzSelect gains an optional `groups` property parallel to `options`: a
non-empty entry renders a non-selectable, muted-caps section-header row
above that option in the open list. The header is plain text, no pill
background, matching the QBZ design rule.
The popup now self-sizes from the list layout's preferred height so the
extra header rows are accounted for. `groups` defaults to empty, so the
backend and sample-rate selects (which never set it) render unchanged.
cc
vicrodh
9f86197f60