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/HorizontalScrollRow.svelte

@@ -127,7 +127,10 @@
   }
   .scroller {
     scroll-snap-type: x mandatory;
-    scrollbar-width: thin;
+    scrollbar-width: none;
+  }
+  .scroller::-webkit-scrollbar {
+    display: none;
   }
   /* Cards are two levels deep (.scroller > .track > .rack > card-wrapper),
      so target them via the rack. flex-shrink: 0 keeps each card at its