Extract PlaylistView's inline bulk action bar into a shared
MultiSelectBar primitive driven by a [BulkAction] model (id / label /
danger / needs-selection) emitting action(id). PlaylistView now declares
its two actions (Select all, Remove) as data; the Favorites tracks tab
will reuse the same bar with its larger action set instead of copying
it. Same visual (count label + bordered/hover buttons, ADR-008).
cc
vicrodh
d531f60c9c