simplified code across the app and consolidated duplicated helpers

lib/api/marianumconnect/queries/submit_feedback/submit_feedback.dart

@@ -5,6 +5,7 @@ import 'dart:typed_data';
 import 'package:device_info_plus/device_info_plus.dart';
 import 'package:package_info_plus/package_info_plus.dart';
 
+import '../../client_platform.dart';
 import '../../marianumconnect_query.dart';
 
 /// Submits user feedback to MarianumConnect (`POST me/feedback`, bearer-auth).
@@ -27,7 +28,7 @@ class SubmitFeedback extends MarianumConnectQuery {
         'message': message,
         'screenshot': ?screenshotBase64,
         'screenshotContentType': screenshot != null ? screenshotContentType : null,
-        'platform': _platform(),
+        'platform': clientPlatform(),
         'appVersion': package.version,
         'appBuild': int.tryParse(package.buildNumber),
         'deviceModel': await _deviceModel(),
@@ -35,12 +36,6 @@ class SubmitFeedback extends MarianumConnectQuery {
     );
   });
 
-  static String? _platform() {
-    if (Platform.isAndroid) return 'android';
-    if (Platform.isIOS) return 'ios';
-    return null;
-  }
-
   static Future<String?> _deviceModel() async {
     try {
       final info = DeviceInfoPlugin();