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/MenuItem.svelte

@@ -5,6 +5,7 @@
 		icon: LucideIcon;
 		label: string;
 		href?: string;
+		target?: string;
 		type?: 'button' | 'submit';
 		reload?: boolean;
 		onclick?: (event: MouseEvent) => void;
@@ -15,6 +16,7 @@
 		icon: Icon,
 		label,
 		href,
+		target,
 		type = 'button',
 		reload = false,
 		onclick,
@@ -22,18 +24,25 @@
 	}: Props = $props();
 
 	const classes = $derived(
-		`flex w-full items-center gap-3 rounded-control px-2 py-2.5 text-left text-base text-fg-2 transition hover:bg-hover ${klass}`
+		`flex w-full items-center gap-3 rounded-control px-2 py-2.5 text-left text-[13.5px] font-medium text-fg-2 transition hover:bg-hover ${klass}`
 	);
 </script>
 
 {#if href}
-	<a {href} data-sveltekit-reload={reload ? '' : undefined} {onclick} class={classes}>
-		<Icon class="h-6 w-6 shrink-0" strokeWidth={2} />
+	<a
+		{href}
+		{target}
+		rel={target === '_blank' ? 'noopener noreferrer' : undefined}
+		data-sveltekit-reload={reload ? '' : undefined}
+		{onclick}
+		class={classes}
+	>
+		<Icon class="h-[18px] w-[18px] shrink-0" strokeWidth={1.8} />
 		{label}
 	</a>
 {:else}
 	<button {type} {onclick} class={classes}>
-		<Icon class="h-6 w-6 shrink-0" strokeWidth={2} />
+		<Icon class="h-[18px] w-[18px] shrink-0" strokeWidth={1.8} />
 		{label}
 	</button>
 {/if}