fix(web): drop-up Add-to-playlist submenu, hide horizontal scroll row scrollbar

- 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.

web/src/lib/components/AddToPlaylistMenu.svelte

@@ -68,7 +68,7 @@
 <div
   role="menu"
   aria-label="Add to playlist"
-  class="absolute right-full top-0 z-30 mr-1 w-56 rounded-md border border-border bg-surface p-1 shadow-lg"
+  class="absolute right-full bottom-0 z-30 mr-1 w-56 rounded-md border border-border bg-surface p-1 shadow-lg"
   onclick={(e) => e.stopPropagation()}
 >
   {#each ownPlaylists as p (p.id)}