add fullscreen mode

lib/main.dart

@@ -6,6 +6,7 @@ import 'package:hive/hive.dart';
 import 'package:logging/logging.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:pdfrx/pdfrx.dart';
+import 'package:flutter_fullscreen/flutter_fullscreen.dart';
 
 import 'login_page.dart';
 
@@ -25,6 +26,10 @@ Future<void> main() async {
     Hive.init(dir.path); // Needed only if not web
   }
 
+  // setup for flutter_fullscreen
+  WidgetsFlutterBinding.ensureInitialized();
+  await FullScreen.ensureInitialized();
+
   runApp(const MyApp());
 }