Refactor preferences service initialization to lazy load SharedPreferences and make registerDefaultServices synchronous

finlog_app/app/lib/main.dart

@@ -9,7 +9,7 @@ Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
 
   // any services
-  await App.registerDefaultServices();
+  App.registerDefaultServices();
 
   final logger = App.service<Logger>();
   logger.debug("[MAIN] Registered all default services");