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/theme/mode.svelte.ts

@@ -0,0 +1,40 @@
+import { browser } from '$app/environment';
+
+export type ThemeName = 'dark' | 'light';
+
+const STORAGE_KEY = 'musify.theme';
+
+function loadInitial(): ThemeName {
+	if (!browser) return 'dark';
+	try {
+		return localStorage.getItem(STORAGE_KEY) === 'light' ? 'light' : 'dark';
+	} catch {
+		return 'dark';
+	}
+}
+
+function applyTheme(theme: ThemeName) {
+	if (!browser) return;
+	document.documentElement.dataset.theme = theme;
+}
+
+class ThemeModeStore {
+	current = $state<ThemeName>(loadInitial());
+
+	constructor() {
+		applyTheme(this.current);
+	}
+
+	toggle() {
+		this.current = this.current === 'dark' ? 'light' : 'dark';
+		applyTheme(this.current);
+		if (!browser) return;
+		try {
+			localStorage.setItem(STORAGE_KEY, this.current);
+		} catch {
+			/* localStorage unavailable (private mode, quota) — preference just won't persist */
+		}
+	}
+}
+
+export const themeMode = new ThemeModeStore();