Replaces the native <select> "Source" control with a labeled FilterSelect pill, matching
the Watch state / Content types pills — one consistent toolbar idiom. Single-select over
the three librarySource values (organic / all / search-only).
Sort and View are intentionally left as-is: Sort is a two-dimensional key+direction control
(plus reshuffle and a tables-only "no sort") shared across five surfaces, and View is already
on the same AnchoredPopover platform with an icon-only trigger tuned for this packed toolbar —
FilterSelect's text trigger would regress it. Neither fits FilterSelect's one-dimensional model.