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/api/tracks/[id]/stream/+server.ts

@@ -1,14 +1,14 @@
 import type { RequestHandler } from './$types';
 import { json } from '@sveltejs/kit';
-import { createApiClient, requireAccessToken, unwrapOrError } from '$lib/server/api';
+import { createApiClient, unwrapOrError } from '$lib/server/api';
 
 export const GET: RequestHandler = async ({ params, locals, fetch }) => {
-	const accessToken = requireAccessToken(locals, 'Inicia sesión para reproducir.');
-
-	const api = createApiClient({ fetch, accessToken });
+	// No hard login gate here: the API itself allows an anonymous request when
+	// AllowAnonymousListening is on, and rejects it with 401 otherwise.
+	const api = createApiClient({ fetch, accessToken: locals.accessToken ?? undefined });
 	const result = await api.GET('/tracks/{id}/stream', {
 		params: { path: { id: params.id } }
 	});
 
-	return json(unwrapOrError(result, 'No se pudo obtener el stream de la pista.'));
+	return json(unwrapOrError(result, 'No se pudo reproducir esta canción.'));
 };