add platforminfo helper

lib/utils/gpx_export.dart

@@ -4,6 +4,7 @@ import 'package:meshcore_open/connector/meshcore_connector.dart';
 import 'package:meshcore_open/connector/meshcore_protocol.dart';
 import 'package:path_provider/path_provider.dart';
 import 'dart:io';
+import '../utils/platform_info.dart';
 
 import 'package:share_plus/share_plus.dart';
 
@@ -109,6 +110,10 @@ class GpxExport {
     String shareText,
     String subject,
   ) async {
+    if (PlatformInfo.isWeb) {
+      debugPrint("GPX export is not supported on Web.");
+      return gpxExportNotAvailable;
+    }
     if (_contacts.isEmpty) {
       debugPrint("No repeaters to export – nothing to share.");
       return gpxExportNoContacts;

lib/utils/platform_info.dart

@@ -0,0 +1,32 @@
+import 'package:flutter/foundation.dart';
+import 'dart:io' show Platform;
+
+/// Utility class to safely check the current platform across web and native.
+///
+/// Using `Platform` from `dart:io` directly on Web causes a crash.
+/// This class handles the `kIsWeb` check first to avoid those crashes.
+class PlatformInfo {
+  /// Whether the app is running in a web browser.
+  static bool get isWeb => kIsWeb;
+
+  /// Whether the app is running on Android.
+  static bool get isAndroid => !kIsWeb && Platform.isAndroid;
+
+  /// Whether the app is running on iOS.
+  static bool get isIOS => !kIsWeb && Platform.isIOS;
+
+  /// Whether the app is running on macOS.
+  static bool get isMacOS => !kIsWeb && Platform.isMacOS;
+
+  /// Whether the app is running on Windows.
+  static bool get isWindows => !kIsWeb && Platform.isWindows;
+
+  /// Whether the app is running on Linux.
+  static bool get isLinux => !kIsWeb && Platform.isLinux;
+
+  /// Whether the app is running on a mobile platform (Android or iOS).
+  static bool get isMobile => isAndroid || isIOS;
+
+  /// Whether the app is running on a desktop platform (macOS, Windows, or Linux).
+  static bool get isDesktop => isMacOS || isWindows || isLinux;
+}