- AddToPlaylistMenu: anchor submenu bottom to parent bottom so it
grows upward (top-0 → bottom-0) — kebab row is usually near the
bottom of the track menu and the submenu kept extending off-screen.
- HorizontalScrollRow: scrollbar-width: none + ::-webkit-scrollbar
display:none. Page arrows already drive the scroll; the scrollbar
was just consuming vertical real estate.
The "Add to playlist…" entry that #372 reserved as a disabled slot
is now active. Submenu lists the operator's own playlists
alphabetically; "New playlist…" toggles an inline create form that
makes the playlist + appends the track in two API calls.
TrackMenu's existing test asserts the entry is enabled and opens the
submenu instead of the previous "is disabled with tooltip" check.
bvandeusen