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/routes/(app)/albums/[id]/components/LibraryPicker.svelte

@@ -28,12 +28,15 @@
 	<SectionHeading title="Tus canciones subidas" />
 	<TrackTable action>
 		{#each library as track, i (track.id)}
-			<TrackRow>
+			{@const active = player.current.id === track.id}
+			<TrackRow {active}>
 				<TrackTitleCell
 					trackId={track.id}
 					title={track.title}
 					artist={track.artist}
+					ownerUserId={track.ownerUserId}
 					explicit={track.isExplicit}
+					{active}
 					onClick={() => playFrom(i)}
 				>
 					{#snippet overlay()}