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/Common/LtsWidgets/lts_base_layout_widget.cpp

@@ -24,26 +24,26 @@
 #include <Lts/Common/ProjectConfig/project_defines.h>
 #include <ngltools/ngltools_dtg.h>
 
-#include <QAbstractItemView>
-#include <QButtonGroup>
-#include <QClipboard>
-#include <QCloseEvent>
-#include <QDebug>
-#include <QImage>
-#include <QMenu>
-#include <QMessageBox>
+#include <QtWidgets/QAbstractItemView>
+#include <QtWidgets/QButtonGroup>
+#include <QtGui/QClipboard>
+#include <QtGui/QCloseEvent>
+#include <QtCore/QDebug>
+#include <QtGui/QImage>
+#include <QtWidgets/QMenu>
+#include <QtWidgets/QMessageBox>
 #include <QMetaMethod>
-#include <QPainter>
-#include <QPixmap>
-#include <QPropertyAnimation>
-#include <QPushButton>
-#include <QScrollArea>
+#include <QtGui/QPainter>
+#include <QtGui/QPixmap>
+#include <QtCore/QPropertyAnimation>
+#include <QtWidgets/QPushButton>
+#include <QtWidgets/QScrollArea>
 #include <QScroller>
 #include <QSvgRenderer>
-#include <QTimer>
-#include <QToolButton>
-#include <QPropertyAnimation>
-#include <QInputDialog>
+#include <QtCore/QTimer>
+#include <QtWidgets/QToolButton>
+#include <QtCore/QPropertyAnimation>
+#include <QtWidgets/QInputDialog>
 
 
 namespace LtsWidgets