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/ui/Button.svelte

@@ -3,7 +3,7 @@
 	import LoaderCircle from '@lucide/svelte/icons/loader-circle';
 
 	interface Props {
-		variant?: 'primary' | 'secondary' | 'subtle' | 'danger';
+		variant?: 'primary' | 'secondary' | 'accent' | 'danger';
 		size?: 'sm' | 'md' | 'lg';
 		type?: 'button' | 'submit';
 		href?: string;
@@ -29,20 +29,22 @@
 	}: Props = $props();
 
 	const sizes = {
-		sm: 'px-4 py-2 text-base',
-		md: 'px-5 py-2.5 text-base',
-		lg: 'px-8 py-3.5 text-base'
+		sm: 'px-4 py-2.5 text-[12.5px]',
+		md: 'px-5 py-3 text-[13px]',
+		lg: 'px-6 py-3.5 text-sm'
 	};
 
+	const subtleButton = 'bg-white/[6%] text-fg-2 hover:bg-white/[9%] hover:text-fg';
+
 	const variants = {
-		primary: 'bg-accent-soft text-on-accent active:scale-[0.97]',
-		secondary: 'bg-bg text-fg ring-1 ring-line hover:bg-surface',
-		subtle: 'bg-white/10 text-fg hover:bg-accent/18',
+		primary: subtleButton,
+		secondary: subtleButton,
+		accent: 'bg-accent-btn text-accent-soft hover:bg-accent-btn-hover',
 		danger: 'bg-danger text-on-accent hover:brightness-110'
 	};
 
 	const classes = $derived(
-		`inline-flex items-center justify-center gap-2 rounded-control font-medium transition focus-visible:ring-2 focus-visible:ring-accent focus-visible:ring-offset-2 focus-visible:ring-offset-bg focus-visible:outline-none disabled:opacity-40 ${sizes[size]} ${variants[variant]} ${klass}`
+		`inline-flex items-center justify-center gap-2 rounded-xl font-semibold transition focus-visible:ring-2 focus-visible:ring-accent focus-visible:ring-offset-2 focus-visible:ring-offset-bg focus-visible:outline-none disabled:opacity-40 ${sizes[size]} ${variants[variant]} ${klass}`
 	);
 </script>