Drop the drone status panel's title bar, default the grid to 3 columns

The title row cost a full line of vertical space for a redundant
label. The close button now floats over the tab row instead, which
reserves 48px on its right so "System Messages" doesn't sit under it.
Also replaced the manually grouped 2/3-column row layout with uniform
3-per-row chunking of a flat field list, matching the user's request
to default to three fields per row.

app/test/widget_test.dart

@@ -30,6 +30,7 @@ import 'package:dmc_app/ui/providers/system_message_log_provider.dart';
 import 'package:dmc_app/ui/providers/telemetry_provider.dart';
 import 'package:dmc_app/transport/mock/mock_flight_controller_link.dart';
 import 'package:dmc_app/ui/widgets/drone_follow_icon.dart';
+import 'package:dmc_app/ui/widgets/drone_status_messages_panel.dart';
 import 'package:dmc_app/ui/widgets/full_value_chart.dart';
 import 'package:dmc_app/ui/widgets/halo_menu.dart';
 import 'package:dmc_app/ui/widgets/header_wind_pill.dart';
@@ -1160,7 +1161,7 @@ void main() {
     // steht im Widget-Baum zuerst.
     await tester.tap(find.byType(PaperPlaneIcon).first);
     await tester.pumpAndSettle();
-    expect(find.text('Drone Status & System Messages'), findsOneWidget);
+    expect(find.byType(DroneStatusMessagesPanel), findsOneWidget);
 
     await tester.tap(find.text('System Messages'));
     await tester.pumpAndSettle();