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/server_databases_model.cpp

@@ -45,7 +45,7 @@ bool ServerDatabasesModel::initModel(const QSqlDatabase &db)
   while (q.next())
   {
     Exercise e;
-    e.m_id        = q.value(0).toInt();
+    e.id        = q.value(0).toInt();
     e.name      = q.value(1).toString();
     e.startTime = q.value(2).toLongLong();
     e.endTime   = q.value(3).toLongLong();
@@ -68,7 +68,7 @@ QVariant ServerDatabasesModel::data(const QModelIndex &index, int role) const
   switch (index.column())
   {
   case Id:
-    return e.m_id;
+    return e.id;
   case Name:
     return QString(e.name);
   case StartTime: