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/components/player/PlayerBar.svelte

@@ -2,44 +2,27 @@
 	import TrackInfo from './TrackInfo.svelte';
 	import TransportControls from './TransportControls.svelte';
 	import SeekBar from './SeekBar.svelte';
-	import VolumeControl from './VolumeControl.svelte';
-	import Alert from '$lib/components/ui/Alert.svelte';
-	import { player } from '$lib/player/player.svelte';
+	import PlayerExtras from './PlayerExtras.svelte';
 </script>
 
-{#if player.error}
-	<div
-		class="fixed inset-x-0 z-40 page-x py-2 md:left-[var(--mf-sidebar-w)] md:z-50"
-		style="bottom:calc(var(--mf-nav-h) + var(--mf-safe-b) + var(--mf-player-h))"
-	>
-		<Alert tone="danger">{player.error}</Alert>
+<div
+	class="animate-enter pointer-events-auto flex items-center gap-4.5 rounded-[18px] border border-hairline bg-[image:var(--mf-bar-bg)] px-4 py-2.75 shadow-player backdrop-blur-[22px] transition-[background] duration-[600ms] sm:hidden"
+>
+	<div class="min-w-0 flex-1">
+		<TrackInfo compact />
 	</div>
-{/if}
+	<TransportControls compact />
+</div>
 
 <div
-	class="animate-enter fixed right-0 left-0 z-40 h-[var(--mf-player-h)] border-t border-line bg-bg md:left-[var(--mf-sidebar-w)] md:z-50"
-	style="bottom:calc(var(--mf-nav-h) + var(--mf-safe-b))"
+	class="animate-enter pointer-events-auto hidden items-center gap-5 rounded-[18px] border border-hairline bg-[image:var(--mf-bar-bg)] px-4 py-2.75 shadow-player backdrop-blur-[22px] transition-[background] duration-[600ms] sm:flex"
 >
-	<div class="absolute inset-x-0 top-0 md:hidden">
-		<SeekBar compact />
-	</div>
-
-	<div class="flex h-full items-center gap-3 page-x md:hidden">
-		<div class="min-w-0 flex-1">
-			<TrackInfo />
-		</div>
-		<TransportControls compact />
-	</div>
-
-	<div
-		class="hidden h-full items-center gap-5 px-8 md:grid"
-		style="grid-template-columns:minmax(200px,1fr) minmax(0,3fr) minmax(200px,1fr)"
-	>
+	<div class="w-64 min-w-0 shrink-0">
 		<TrackInfo />
-		<div class="flex flex-col items-center gap-2">
-			<TransportControls />
-			<SeekBar />
-		</div>
-		<VolumeControl />
 	</div>
+	<div class="flex min-w-0 flex-1 flex-col items-center gap-2">
+		<TransportControls />
+		<SeekBar />
+	</div>
+	<PlayerExtras />
 </div>