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/player/PlayerDock.svelte

@@ -0,0 +1,29 @@
+<script lang="ts">
+	import PlayerBar from './PlayerBar.svelte';
+	import TabsBar from '../TabsBar.svelte';
+	import Alert from '$lib/components/ui/Alert.svelte';
+	import { player } from '$lib/player/player.svelte';
+	import type { SessionUser } from '$lib/types';
+
+	interface Props {
+		user: SessionUser | null;
+	}
+
+	let { user }: Props = $props();
+
+	const hasTrack = $derived(player.currentId !== null);
+</script>
+
+<div
+	class="pointer-events-none fixed inset-x-0 bottom-0 z-40 flex flex-col gap-2.5 px-4 pb-4 lg:left-[var(--mf-sidebar-w)]"
+>
+	{#if player.error}
+		<div class="pointer-events-auto">
+			<Alert tone="danger">{player.error}</Alert>
+		</div>
+	{/if}
+	{#if hasTrack}
+		<PlayerBar />
+	{/if}
+	<TabsBar {user} />
+</div>