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/TetraIF/LogView/LogViewGui.cpp

@@ -19,28 +19,28 @@
 #include "LogViewTelegramDialog.hpp"
 #include "LogViewOptionDialog.hpp"
 #include <CoPrtCnv/CoPrtCnvRadioTelegram.hpp>
-#include <QDir>
-#include <QFile>
-#include <QTimer>
-#include <QAction>
-#include <QApplication>
-#include <QCheckBox>
+#include <QtCore/QDir>
+#include <QtCore/QFile>
+#include <QtCore/QTimer>
+#include <QtGui/QAction>
+#include <QtWidgets/QApplication>
+#include <QtWidgets/QCheckBox>
 #include <QDesktopWidget>
-#include <QFileDialog>
-#include <QGroupBox>
-#include <QHeaderView>
-#include <QJsonArray>
-#include <QLabel>
-#include <QMessageBox>
-#include <QScreen>
-#include <QSortFilterProxyModel>
-#include <QSplitter>
-#include <QStatusBar>
-#include <QTableView>
-#include <QToolBar>
-#include <QToolBox>
-#include <QDateTime>
-#include <QVBoxLayout>
+#include <QtWidgets/QFileDialog>
+#include <QtWidgets/QGroupBox>
+#include <QtWidgets/QHeaderView>
+#include <QtCore/QJsonArray>
+#include <QtWidgets/QLabel>
+#include <QtWidgets/QMessageBox>
+#include <QtGui/QScreen>
+#include <QtCore/QSortFilterProxyModel>
+#include <QtWidgets/QSplitter>
+#include <QtWidgets/QStatusBar>
+#include <QtWidgets/QTableView>
+#include <QtWidgets/QToolBar>
+#include <QtWidgets/QToolBox>
+#include <QtCore/QDateTime>
+#include <QtWidgets/QVBoxLayout>
 #include <nglapplication/nglapplication.h>
 
 #include "LogViewInjectionThread.hpp"