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/AlbumForm.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
 	import { untrack } from 'svelte';
 	import { enhance } from '$app/forms';
+	import Disc3 from '@lucide/svelte/icons/disc-3';
 	import ImageDropzone from './ImageDropzone.svelte';
 	import Button from './Button.svelte';
 	import Field from './Field.svelte';
@@ -59,11 +60,18 @@
 			if (result.type === 'success') onSuccess?.();
 		};
 	}}
-	class="mt-4 w-full max-w-2xl space-y-4"
+	class="mt-5 w-full max-w-2xl space-y-5"
 >
 	<div class="flex flex-col items-stretch gap-5 sm:flex-row sm:gap-8">
-		<Field label="Portada" optional={!requireCover}>
-			<ImageDropzone name="cover" fallbackUrl={coverFallbackUrl} required={requireCover} />
+		<Field>
+			<ImageDropzone
+				name="cover"
+				fallbackUrl={coverFallbackUrl}
+				required={requireCover}
+				icon={Disc3}
+				gradient
+				class="h-36 w-36 rounded-[16px]"
+			/>
 		</Field>
 
 		<div class="flex flex-1 flex-col gap-4">
@@ -78,7 +86,7 @@
 				/>
 			</Field>
 
-			<Field label="Año de publicación" for="album-year" optional>
+			<Field label="Año de publicación" for="album-year">
 				<Input
 					id="album-year"
 					name="releaseYear"
@@ -92,7 +100,7 @@
 		</div>
 	</div>
 
-	<Field label="Descripción" for="album-description" optional>
+	<Field label="Descripción" for="album-description">
 		<Textarea
 			id="album-description"
 			name="description"