Render unknown URLs inside the app shell and move ListeningStats to the domain types

Add catch-all routes so unknown pages 404 inside the (app) layout and unknown
/api URLs return a JSON 404 instead of redirecting to the login page. Restore
the full root error page.

web-player/src/routes/(app)/[...rest]/+page.server.ts

@@ -0,0 +1,6 @@
+import { error } from '@sveltejs/kit';
+import type { PageServerLoad } from './$types';
+
+export const load: PageServerLoad = () => {
+	error(404, 'Página no encontrada');
+};