library-filter is the only control in the app that calls
setSelectedLibrary, and the phone already hid it with a comment saying
it was "reachable from the drawer's Settings". It was not: Settings adds,
removes, renames and scans libraries, and does not set the view filter,
which is a different thing -- it decides what Albums, Artists and Genres
show. A phone therefore inherited whatever a desktop session last chose
and could neither change nor see it, which is #24's sentence broken in
the band it was written for.
It is a second *placement* of the same component, not a second control,
and it is at every width rather than below 600px. A phone-only copy is
the cheaper answer and is the fault rather than the fix: "where do I
change which library I am browsing" having two answers by viewport is
exactly what one control in two places avoids.
Closes#148