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/lib/ui/widgets/bottom_stats_bar.dart

@@ -10,7 +10,7 @@ import '../dmc_colors.dart';
 import '../providers/active_drone_profile_provider.dart';
 import '../providers/altitude_profile_provider.dart';
 import '../providers/mission_meta_provider.dart';
-import 'drone_status_warnings_panel.dart';
+import 'drone_status_messages_panel.dart';
 import 'missions_drones_panel.dart';
 import 'mountain_peak_icon.dart';
 import 'paper_plane_icon.dart';
@@ -90,9 +90,10 @@ class BottomStatsBar extends ConsumerWidget {
   /// Nur im Fly-Modus gesetzt (Doku: "im fly screen den warnings button
   /// durch einen wp send button ersetzen") - wenn gesetzt, ersetzt der
   /// Sende-Knopf (Papierflieger, horizontal, pink) den runden Warnungs-
-  /// Knopf komplett, unabhaengig von [warnings]. Warnungen/Ereignis-Log
-  /// bleiben im Fly-Modus weiterhin ueber die Drohnen-Status-Pille
-  /// erreichbar (dort als eigener Tab), siehe DroneStatusWarningsPanel.
+  /// Knopf komplett, unabhaengig von [warnings]. System Messages (Doku:
+  /// "aendere das warnings Menü in System Messages") bleiben im Fly-Modus
+  /// weiterhin ueber die Drohnen-Status-Pille erreichbar (dort als eigener
+  /// Tab), siehe DroneStatusMessagesPanel.
   final VoidCallback? onSendTap;
 
   /// Zeigt einen Ladeindikator statt des Papierflieger-Icons und ignoriert
@@ -187,7 +188,7 @@ class BottomStatsBar extends ConsumerWidget {
                               // Profile werden waehrend des Fluges ohnehin
                               // nicht gewechselt.
                               onTap: () => Navigator.of(context).push(MaterialPageRoute(
-                                builder: (_) => const DroneStatusWarningsPanel.status(),
+                                builder: (_) => const DroneStatusMessagesPanel.status(),
                               )),
                             )
                           : _NameChip(