fix: Tighten device settings layout

test/providers/channels_provider_test.dart

@@ -0,0 +1,25 @@
+import 'dart:typed_data';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:meshcore_sar_app/providers/channels_provider.dart';
+
+void main() {
+  group('ChannelsProvider device sync preparation', () {
+    test('clears runtime channel state before sync', () {
+      final provider = ChannelsProvider();
+
+      provider.addOrUpdateChannel(
+        index: 2,
+        name: 'Ops',
+        secret: Uint8List.fromList(List<int>.filled(16, 7)),
+      );
+      provider.selectChannel(2);
+
+      provider.prepareForDeviceSync();
+
+      expect(provider.channels, isEmpty);
+      expect(provider.selectedChannelIndex, 0);
+      expect(provider.selectedChannel, isNull);
+    });
+  });
+}