replaced account data singleton with a session model

lib/push/push_device_info.dart

@@ -0,0 +1,15 @@
+import 'dart:io';
+
+import 'package:package_info_plus/package_info_plus.dart';
+
+/// Platform value MarianumConnect expects in push registrations.
+String get pushPlatform => Platform.isIOS ? 'ios' : 'android';
+
+/// App version sent along with push registrations; null when unavailable.
+Future<String?> pushAppVersion() async {
+  try {
+    return (await PackageInfo.fromPlatform()).version;
+  } on Object {
+    return null;
+  }
+}