Qt6 API fixes: QJsonObject and QJsonDocument serialization

- training_area_telegrams.cpp:3168: Fixed QJsonObject initializer list syntax
  - Changed QJsonObject({{...}}) to QJsonObject{{...}} (double braces)
  - Changed header.toJson() to header().toJson() (method call)

- track_content_widget.cpp:37,51: Fixed QJsonDocument serialization
  - Replaced toBinaryData() with toJson(QJsonDocument::Compact)
  - Replaced fromBinaryData() with fromJson()
  - Qt6 removed binary serialization methods

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

qt6-after/qt6-migrated-legatus/Lts/Proxies/TrainingAreaBase/training_area_telegrams.cpp

@@ -3165,14 +3165,14 @@ BatteryAlarm BatteryAlarm::fromJson(const QJsonObject &obj)
 
 QJsonObject BatteryAlarm::toJson() const
 {
-  return QJsonObject({{QStringLiteral("header"), header.toJson()},
+  return QJsonObject{{QStringLiteral("header"), header().toJson()},
                       {QStringLiteral("id"), id},
                       {QStringLiteral("description"), description},
                       {QStringLiteral("acknowledge"), acknowledge},
                       {QStringLiteral("condition"), condition},
                       {QStringLiteral("uniqueAlarmNumber"), uniqueAlarmNumber},
                       {QStringLiteral("alarmTime"), alarmTime}
-                     });
+                     };
 }
 
 ServiceControl ServiceControl::fromJson(const QJsonObject &obj)