Adds a per-list filter to the board action bar, visible only in
List View. Mirrors the existing transient label/member filter
pattern: filterLists is a many-relation on the Board ORM model,
toggled via entry actions and reset on board navigation. Empty
selection keeps the current behavior; non-empty selection shows
only cards whose listId is in the chosen set. Filter UI is hidden
in Kanban/Grid views where columns already convey the same info.
Closes#1524
Symon
401c0412cb