Checkpoint web-player design-system refactor and backend track genre tagging

Advances the ongoing token/componentization cleanup (anchored player dock,
border-based panels instead of floating shadows, corrected light-mode
accent/gradient tokens) alongside in-progress backend support for track
genre tags.

web-player/src/lib/mixes.ts

@@ -13,7 +13,8 @@ export function mixItemTarget(item: MixItem): TrackTarget {
 		track: {
 			id: item.trackId,
 			title: item.title,
-			artist: item.artist
+			artist: item.artist,
+			listensCount: item.listensCount
 		}
 	};
 }