Qt6 Migration: Complete migration with DDS/RTI support and build validation

Major Changes:
- Merged latest Qt5 devel content from dlbo (292 files changed, 7 new dirs)
- Consolidated forward-declarations and include folders
- Removed unneeded modules per Niklas' repo check list

Build System Fixes:
- Fixed CMake VERSION_GREATER syntax in ParticipantManagement/CMakeLists.txt
- Added VLC packages (libvlc-dev, vlc-plugin-base) to docker_build.sh
- Added PostgreSQL dev packages (libpq-dev, postgresql-server-dev-all) to Dockerfile
- Fixed locale warnings (ANSI_X3.4-1968 → C.UTF-8)
- Fixed ArcGIS SDK path warnings when BUILD_ARCGIS=OFF

Code Generation Fixes:
- Fixed IDL enum collisions (PortType→CorePortType/DdsutPortType, PdmEventType)
- Fixed Grantlee template svc_translation.cpp.grantlee:
  - Changed {{ idl_enum.name }}_def:: to {{ idl_enum.name }}::
  - Fixed .underlying() calls for C++11 scoped enums (enum class)
- Removed generated files from repo (moc_*, *_dtc.h, *_ftc.h)

Validation:
- BUILD_RTI=ON: SUCCESS
- BUILD_RTI=OFF: SUCCESS
- C++17 standard maintained for RTI 7.7 compatibility
- Ubuntu 26.04 Docker environment verified

Remaining Warnings (expected):
- BgViewer, KDChart, KDReports, Poppler-Qt6 not found (optional features)

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

qt5-before/dlbo/Lts/Common/LtsWebSocket/client_message.cpp

@@ -0,0 +1,44 @@
+/**
+  * @RDE_HEADER@
+  * LTS web socket server - Abstract Client Message
+  * $Id$
+  * $HeadURL$
+  * $Author$
+  * Created by Philipp Dassow, SLST, 2017-11-28
+  */
+#include "client_message.h"
+
+#include "json_keys.h"
+
+#include <QJsonDocument>
+
+namespace LtsWebSocket
+{
+
+// ######## AbstractClientMessage end ########
+
+// ######## InvalidMessage begin ########
+InvalidMessage::InvalidMessage(ReplyHandler *client, const QString &uuid, const QString &errorText)
+  : AbstractClientMessage(client, QString(), 1, uuid) // Check if 1 is feasible - or if it needs to be a part of InvalidMessage
+  , m_errorText(errorText)
+{}
+
+void InvalidMessage::process()
+{
+  ErrorMessage::ErrorData errorData;
+
+  errorData.errorClass    = 1; // ??????????
+  errorData.errorMessage  = m_errorText;
+  errorData.uuid          = m_uuid;
+
+  m_client->addReply(new ErrorMessage(errorData));
+}
+
+bool InvalidMessage::hasValidData() const
+{
+  // always true because there is no data part
+  return true;
+}
+// ######## InvalidMessage end ########
+
+} // namespace LtsWebSocketServer