Merge feature/qt6-migration-basis-modules-services into feature/qt6-migration-basis-modules

Resolves 17 conflicts against legacy Qt5 semantics; validates with BUILD_RTI=ON BUILD_GRANTLEE=ON.

qt6-after/qt6-migrated-legatus/.forward-declarations/include/FileManagement/flm_ftc.h

@@ -0,0 +1,20 @@
+/**
+  * @RDE_HEADER@
+  * FileManagement Topic Client Stub (BUILD_RTI=OFF)
+  * Normally generated from flm_service.xml by DDS Code Generator
+  */
+
+#pragma once
+
+#include <memory>
+
+namespace FileManagement
+{
+namespace Interface
+{
+
+// Forward declaration - actual implementation provided by DDS when BUILD_RTI=ON
+class Ftc;
+
+} // namespace Interface
+} // namespace FileManagement