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/+page.svelte

@@ -35,7 +35,7 @@
 	</PageHeader>
 
 	{#if items.length > 0}
-		<MediaGrid class="mt-9">
+		<MediaGrid class="mt-7 sm:mt-8">
 			{#each items as album, i (album.id)}
 				<AlbumCard
 					id={album.id}
@@ -55,10 +55,7 @@
 			description="Crea el primero y añádele las canciones que hayas subido."
 		>
 			{#snippet actions()}
-				<Button onclick={() => (creating = true)}>
-					<Plus class="h-4 w-4" strokeWidth={2} />
-					Crear álbum
-				</Button>
+				<Button onclick={() => (creating = true)}>Crear álbum</Button>
 			{/snippet}
 		</EmptyState>
 	{/if}