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/domain/telemetry/telemetry_field_status.dart

@@ -80,7 +80,7 @@ TelemetryFieldStatus computeTelemetryFieldStatus({
       profile.gpsSatRedMin,
     ),
     // Ohne Fix ist der HDOP-Wert bedeutungslos/veraltet (siehe Anzeige in
-    // drone_status_warnings_panel.dart, die dafuer bereits '—' zeigt) - dann
+    // drone_status_messages_panel.dart, die dafuer bereits '—' zeigt) - dann
     // unabhaengig vom Zahlenwert rot statt eines irrefuehrend guten Signals.
     hdop: hasFix
         ? _levelLowerIsBetter(hdop, profile.hdopGreenMax, profile.hdopRedMax)