Qt6 migration: Fix BUILD_RTI=OFF build errors in TrainingAreaBase

- training_area_telegrams.cpp: Fixed QJsonObject initializer syntax (Qt6 requires {{}} not ({}))
- training_area_telegrams.cpp: Fixed fromJson() methods to access m_* members directly
- training_area_telegrams.cpp: Fixed brace mismatches in multiple toJson() methods
- training_area_telegrams.h: Changed Header struct to public members for consistency
- tx_mixin.cpp: Fixed getEquipmentNumber() template for direct member access
- lts_coordinate.cpp: Added missing #include <iomanip>
- MIGRATION_STATUS.md: Added migration progress tracking document

C++17 constraint enforced due to RTI Connext DDS 7.7.0 incompatibility with C++20+

Build status: BUILD_RTI=OFF successful (0 errors, warnings only)

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

qt6-after/qt6-migrated-legatus/Lts/Services/AreaEffectSimulation/ModuleTest_EffectCluster/effect_cluster_module_test.cpp

@@ -18,14 +18,14 @@
 // PPM
 #include "ParticipantManagement/ppm_ftc_types.h"
 #include "TrainingAreaBase/tab.hpp"
-#include <QDateTime>
-#include <QDebug>
-#include <QFile>
-#include <QJsonArray>
-#include <QJsonDocument>
-#include <QTimer>
-#include <QVector>
-#include <QXmlStreamReader>
+#include <QtCore/QDateTime>
+#include <QtCore/QDebug>
+#include <QtCore/QFile>
+#include <QtCore/QJsonArray>
+#include <QtCore/QJsonDocument>
+#include <QtCore/QTimer>
+#include <QtCore/QVector>
+#include <QtCore/QXmlStreamReader>
 
 #include <iostream>
 

qt6-after/qt6-migrated-legatus/Lts/Services/AreaEffectSimulation/ModuleTest_EffectCluster/effect_cluster_module_test.h

@@ -30,7 +30,7 @@
 
 #include <TrainingAreaBase/tab_dts.h>
 
-#include <QCoreApplication>
+#include <QtCore/QCoreApplication>
 
 #include <QtTest/QTest>