Add likes, follows and playlist visibility; redesign web-player UI

Backend:
- New Likes feature (toggle/get liked tracks) and endpoints
- User follow/unfollow, listening stats, public user profile
- Playlist visibility (public/private) support
- Various auth and DTO/response adjustments to support the above

Frontend (web-player):
- New design system pass: theme tokens/mode (light/dark), glass menu,
  tabs bar, player dock/extras/queue components, mix tiles, artist link
- New routes: Liked, public user profile (/u/[id]), likes API proxy
- Search refactor: shared SearchBox component used by TopBar and
  MobileHeader (search now reachable on mobile), live results as you
  type instead of requiring Enter, dropped the "Buscando…" quick-result
  preview
- Removed now-unused components (MobileNav, CoverBadge, MixBentoTile,
  PlayPauseOverlay, SuggestionsTable, userDirectory)
- Design handoff reference docs added under web-player/design_handoff_musify_player
  and web-player/docs/design-system-refactor-plan.md

web-player/src/lib/tracks.ts

@@ -22,6 +22,10 @@ export function targetArtist(target: TrackTarget): string | undefined {
 	return (target.kind === 'youtube' ? target.song.artist : target.track.artist) ?? undefined;
 }
 
+export function targetOwnerUserId(target: TrackTarget): string | number | undefined {
+	return target.kind === 'youtube' ? undefined : (target.track.ownerUserId ?? undefined);
+}
+
 export function targetExplicit(target: TrackTarget): boolean {
 	return target.kind === 'youtube' ? target.song.isExplicit : (target.track.isExplicit ?? false);
 }
@@ -76,7 +80,8 @@ export function targetForQueueItem(item: QueueItem): TrackTarget {
 					title: item.title,
 					artist: item.artist,
 					source: 'Local',
-					isExplicit: item.explicit
+					isExplicit: item.explicit,
+					ownerUserId: item.ownerUserId
 				}
 			};
 }