- Replace all Qt5:: target references with Qt6:: in 26 CMakeLists.txt files
- Add missing participant_info_gui_element_interface.h to ParticipantManagement plugin
Qt6 migration: All CMake target_link_libraries now use Qt6::Core, Qt6::Widgets,
Qt6::Network instead of Qt5:: equivalents.
Validated with BUILD_RTI=ON and BUILD_RTI=OFF - both builds successful.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>