Rename the Fly-mode Warnings tab to System Messages, log connection/upload events

Renames DroneEvent/DroneEventSeverity/droneEventLogProvider/
DroneStatusWarningsPanel to SystemMessage/SystemMessageSeverity/
systemMessageLogProvider/DroneStatusMessagesPanel throughout, matching
what the tab now actually shows - general system messages, not just
drone-health warnings.

Adds a new SystemMessageSeverity.info level (blue) for messages that
aren't a warning/error, and three new message sources on top of the
existing battery/failsafe detection:
- "Connected", logged the first time telemetryProvider produces a frame
  after having none - the mirror image of the existing "Connection lost"
  detection (which already fires on the first stream error after having
  had data), so no new transport-specific dependency was needed.
- "Connection type changed to X", from watching connectionSettingsProvider
  (skips the initial load so it doesn't fire on every app start).
- "Mission sent (N waypoints)" / "Mission upload failed: ...", logged
  from FlyScreen's send handler via a new public log() method on the
  notifier, alongside the existing snackbar.

Verified on the Pixel_10a emulator: entering Fly mode logs "Connected"
once the mock telemetry starts, and tapping the send button logs
"Mission sent (3 waypoints)" right after the snackbar.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/test/widget_test.dart

@@ -33,6 +33,7 @@ import 'package:dmc_app/ui/widgets/header_wind_pill.dart';
 import 'package:dmc_app/ui/widgets/map_search_controls.dart';
 import 'package:dmc_app/ui/providers/map_controller_provider.dart';
 import 'package:dmc_app/ui/widgets/missions_drones_panel.dart';
+import 'package:dmc_app/ui/widgets/paper_plane_icon.dart';
 import 'package:dmc_app/ui/widgets/reticle_button.dart';
 import 'package:dmc_app/ui/widgets/waypoint_chip.dart';
 import 'package:dmc_app/ui/widgets/waypoint_list_panel.dart';
@@ -1001,6 +1002,43 @@ void main() {
     await _stopTelemetry(container);
   });
 
+  testWidgets(
+      'Drohnen-Status-Pille oeffnet "Drone Status & System Messages", '
+      'System-Messages-Tab zeigt "Connected" nach der ersten Telemetrie',
+      (tester) async {
+    final container = _testContainer();
+    addTearDown(container.dispose);
+
+    await tester.pumpWidget(
+      UncontrolledProviderScope(
+        container: container,
+        child: BlocProvider(
+          create: (_) => AppModeCubit(),
+          child: const MaterialApp(home: AppShell()),
+        ),
+      ),
+    );
+    await tester.pump();
+
+    await tester.tap(find.text('Fly'));
+    await tester.pump();
+    // MockFlightControllerLink tickt erst nach 1s (siehe oben).
+    await tester.pump(const Duration(seconds: 1, milliseconds: 100));
+
+    // Zwei PaperPlaneIcon-Instanzen im Fly-Fusszeile (Drohnen-Status-Pille
+    // UND der pinke Sende-Knopf, siehe bottom_stats_bar.dart) - die Pille
+    // steht im Widget-Baum zuerst.
+    await tester.tap(find.byType(PaperPlaneIcon).first);
+    await tester.pumpAndSettle();
+    expect(find.text('Drone Status & System Messages'), findsOneWidget);
+
+    await tester.tap(find.text('System Messages'));
+    await tester.pumpAndSettle();
+    expect(find.text('Connected'), findsOneWidget);
+
+    await _stopTelemetry(container);
+  });
+
   testWidgets('Fit-Button im Fly-Modus ohne Wegpunkte zeigt Hinweis statt Absturz',
       (tester) async {
     final container = _testContainer();