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/Plugins/InfrastructureManagement/Gui/ResourceManagement/Timeline/ism_plan_tln_delegate.cpp

@@ -2,9 +2,9 @@
 
 #include <LtsTimeline/timeline_header_view.h>
 
-#include <QGuiApplication>
-#include <QModelIndex>
-#include <QPainter>
+#include <QtGui/QGuiApplication>
+#include <QtCore/QModelIndex>
+#include <QtGui/QPainter>
 #include <QStyleOptionViewItem>
 
 namespace InfrastructureManagement

qt6-after/qt6-migrated-legatus/Lts/Plugins/InfrastructureManagement/Gui/ResourceManagement/Timeline/ism_plan_tln_dialog.cpp

@@ -15,7 +15,7 @@
 #include <InfrastructureManagement/ism_dtc.h>
 #include <InfrastructureManagement/ism_enums.hpp>
 #include <InfrastructureManagement/settings.h>
-#include <QScrollBar>
+#include <QtWidgets/QScrollBar>
 
 namespace InfrastructureManagement
 {

qt6-after/qt6-migrated-legatus/Lts/Plugins/InfrastructureManagement/Gui/ResourceManagement/Timeline/ism_plan_tln_dialog.h

@@ -17,7 +17,7 @@
 #include <Plugins/InfrastructureManagement/Data/ism_data_plugin.h>
 #include <Plugins/InfrastructureManagement/ism_resource_management_gui_plugin_interface.h>
 
-#include <QDateTime>
+#include <QtCore/QDateTime>
 
 namespace Ui
 {

qt6-after/qt6-migrated-legatus/Lts/Plugins/InfrastructureManagement/Gui/ResourceManagement/Timeline/ism_plan_tln_model.cpp

@@ -4,7 +4,7 @@
 #include "ism_plan_tln_model.h"
 #include <utility>
 #include <LtsWidgets/lts_message_dialog.h>
-#include <QDateTime>
+#include <QtCore/QDateTime>
 
 
 using namespace LtsTimeline;