Add anonymous listening support and redesign web-player UI

Backend:
- Expose GET /config/playback so the frontend can detect whether
  anonymous listening is enabled without requiring auth
- Wire anonymous access through track streaming and YouTube resolve flows

Frontend:
- Allow browsing/listening without a session when the backend enables it
- Redesign Inicio, Sidebar and top bar with a new dark theme, typography,
  and layout (top bar with live quick-search, sticky/blurred on scroll)
- Populate Top música, Popular and Recomendados with real Musify +
  YouTube Music data instead of placeholders
- Various shape, spacing, color and animation refinements across the
  redesigned components

web-player/src/routes/+layout.server.ts

@@ -1,11 +1,14 @@
 import { redirect } from '@sveltejs/kit';
 import type { LayoutServerLoad } from './$types';
+import { getAllowAnonymousListening } from '$lib/server/playbackConfig';
 
 const PUBLIC_PATHS = new Set(['/login']);
 
-export const load: LayoutServerLoad = ({ locals, url }) => {
-	if (!locals.user && !PUBLIC_PATHS.has(url.pathname)) {
+export const load: LayoutServerLoad = async ({ locals, url, fetch }) => {
+	const allowAnonymousListening = await getAllowAnonymousListening(fetch);
+
+	if (!locals.user && !allowAnonymousListening && !PUBLIC_PATHS.has(url.pathname)) {
 		redirect(302, `/login?returnTo=${encodeURIComponent(url.pathname + url.search)}`);
 	}
-	return { user: locals.user };
+	return { user: locals.user, allowAnonymousListening };
 };