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/AudioVideoManagement/Gui/AVMenuEdit/TopicEditor/avm_sequence_model.cpp

@@ -4,8 +4,8 @@
 #include "avm_sequence_model.h"
 #include <utility>
 
-#include <QJsonObject>
-#include <QColor>
+#include <QtCore/QJsonObject>
+#include <QtGui/QColor>
 #include <chrono>
 
 

qt6-after/qt6-migrated-legatus/Lts/Plugins/AudioVideoManagement/Gui/AVMenuEdit/TopicEditor/avm_sequence_model.h

@@ -6,7 +6,7 @@
 #include <AudioVideoManagement/logger.h>
 #include <LtsWidgets/lts_abstract_table_model.h>
 #include <LtsWidgets/lts_column_filter_proxy_model.h>
-#include <QJsonArray>
+#include <QtCore/QJsonArray>
 
 namespace AudioVideoManagement
 {

qt6-after/qt6-migrated-legatus/Lts/Plugins/AudioVideoManagement/Gui/AVMenuEdit/TopicEditor/topic_editor.cpp

@@ -10,7 +10,7 @@
 #include <AudioVideoManagement/ava_session.h>
 #include <AudioVideoManagement/avs_dialog.h>
 #include <LtsSession/lts_session_data.h>
-#include <QJsonArray>
+#include <QtCore/QJsonArray>
 #include <TopicEditorBase/topic_previewer.h>
 #include <boost/optional.hpp>
 #include <cmath>