Add a Bootstrap-style `sm` flag to the shared toolbar primitives
(QbzSelect, ExpandableSearch, ToggleButton) — default stays the standard
size (Settings keeps it), and the favorites toolbar opts in (genre /
group / sort / search / grid-list now ~30px). FavGenreButton + the
favorites grid/list ViewToggle shrink to match. Also vertically center
the MultiSelectBar action buttons (only the count was centered before).
cc