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

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web-player/src/routes/login/+page.svelte

@@ -12,14 +12,15 @@
 </svelte:head>
 
 <div class="relative grid min-h-screen place-items-center overflow-hidden bg-bg px-6 text-fg">
-	<div
-		class="pointer-events-none absolute inset-0"
-		style="background:radial-gradient(ellipse 46rem 28rem at 50% 36%, color-mix(in oklch, var(--color-accent), transparent 82%), transparent 70%)"
-	></div>
+	<div class="pointer-events-none absolute inset-0" style="background:var(--mf-ambient)"></div>
 
 	<div class="relative flex w-full max-w-4xl flex-col items-center gap-12 text-center">
-		<div class="font-display text-[clamp(1.5rem,3vw,2.5rem)] font-semibold tracking-tight">
-			Musify
+		<div class="flex items-center gap-3">
+			<span class="h-8 w-8 rounded-xl bg-[image:var(--mf-logo-grad)] shadow-[var(--mf-logo-glow)]"
+			></span>
+			<span class="font-display text-[clamp(1.5rem,3vw,2.5rem)] font-semibold tracking-tight">
+				Musify
+			</span>
 		</div>
 
 		<div class="animate-enter flex flex-col items-center gap-5">
@@ -39,7 +40,7 @@
 			<Button
 				href={`/auth/login?mode=register&${returnParam}`}
 				reload
-				variant="subtle"
+				variant="secondary"
 				size="lg"
 				class="w-full"
 			>