refactor: clean up verbose migration comments

Remove redundant Qt6 migration comments that restate obvious API changes:
- QtConcurrent::run parameter order explanations (preserved where lambda wrapping needed)
- QStringRef/QStringView API changes (shortened to essential info)
- QComboBox::activated signal signature change
- QMap::unite() removal semantics
- QAction include path change
- QMouseEvent/QWheelEvent position() API
- QList/QVector equivalence in Qt6
- QFuture continuation API
- Code generation comments

Preserved comments explaining non-obvious Qt6 behavior or necessary
API migration details.

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

qt6-after/qt6-migrated-legatus/Lts/Services/InfrastructureManagement/handler_main_structure_element.cpp

@@ -94,7 +94,6 @@ bool HandlerMainStructureElement::init()
   }
 
   // add structure elements to global map for lookup (e.g. in 'add Footprints to MSE objects')
-  // Qt6: QMap::unite removed -> merge manually (unite semantics: overwrite existing keys)
   for (ObjectMainStructureElement *objMse : std::as_const(m_objectMainStructureElementMap))
   {
     const auto &seMap = objMse->getStructureElements();