Migrate LTS Tools Group 6 (D&L) to Qt6

Build script changes:
- Add --group6/--no-group6 argument support to new_docker_build.sh
- Add GROUP6_TARGETS array with 11 LTS tools
- Add BUILD_GROUP6 environment variable export
- Add GROUP6 build invocation in run_build_group function

Test infrastructure:
- Create CTest test files for all 11 Group 6 tools
- Add exclusion filters in tests/CMakeLists.txt for conditional builds
- Tests follow gtest pattern: CompilationStub, Qt6ApiCompatibility, BasicFunctionality

Qt6 migration bug fixes:
- DBAdministration: Fix m_id → id member access (3 files)
- DBAdministration: Add missing QFile include in showLogFile.cpp
- DBUpdate: Add CMAKE_AUTOUIC_SEARCH_PATHS for ui/ directory
- DBUpdate: Fix m_id → id, m_description → description (3 files)

Build validation:
- DBAdministration, DBOperatorSettingsRemover, DBUpdate build successfully
- Remaining tools blocked by pre-existing Group 3 (ExerciseManagement) errors
- Policy checks passed

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

qt6-after/qt6-migrated-legatus/Lts/Tools/DBAdministration/db_administration.cpp

@@ -203,7 +203,7 @@ void DBAdministration::onCopyButtonClicked()
 {  
   disableButtons();
   auto exercise = m_serverDatabasesModel->getRowData(m_proxyModelServer->mapToSource(m_ui->tableViewServerDatabases->currentIndex()).row());
-  m_copyExercise->doCopy(exercise.m_id);
+  m_copyExercise->doCopy(exercise.id);
   if (!m_progressDialog)
     m_progressDialog = new QProgressDialog(this);
   m_progressDialog->setLabelText(tr("Copying database..."));
@@ -234,7 +234,7 @@ void DBAdministration::onDropDbFinished(int exitCode, QProcess::ExitStatus exitS
   if (bRemoveLocal)
   {
     NSqlQuery q(m_copyExercise->evaluationDb());
-    QString stmt = QStringLiteral("DELETE FROM local_databases WHERE id = ") + QString::number(m_localDatabaseToRemove.m_id);
+    QString stmt = QStringLiteral("DELETE FROM local_databases WHERE id = ") + QString::number(m_localDatabaseToRemove.id);
     if (!q.exec(stmt))
       QMessageBox::critical(this, tr ("Remove Database"), tr("Database entry cannot be removed."), QMessageBox::Ok);
     else