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/lib/components/ui/TrackIndexCell.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
 	import Play from '@lucide/svelte/icons/play';
-	import NowPlaying from './NowPlaying.svelte';
+	import EqBars from './EqBars.svelte';
 
 	interface Props {
 		index: number;
@@ -16,10 +16,10 @@
 	type="button"
 	onclick={onToggle}
 	aria-label={active && playing ? 'Pausar' : 'Reproducir'}
-	class="relative grid h-8 w-8 place-items-center overflow-hidden rounded text-sm text-muted"
+	class="relative grid h-8 w-8 place-items-center rounded text-xs text-muted tabular-nums"
 >
 	{#if active}
-		<NowPlaying paused={!playing} />
+		<EqBars paused={!playing} />
 	{:else}
 		<span class="group-hover:hidden">{index + 1}</span>
 		<Play class="hidden h-3.5 w-3.5 text-fg group-hover:block" fill="currentColor" />