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/tests/test_mathutils.cpp

@@ -71,7 +71,6 @@ TEST(MathUtilsTest, Polygon_Area_Calculation)
 // Test MathUtils Qt6 QList/QVector compatibility
 TEST(MathUtilsTest, Qt6_List_Vector_Compatibility)
 {
-    // Qt6: QList and QVector are identical
     // This test verifies that ambiguous overloads are resolved
     
     QList<double> list = {1.0, 2.0, 3.0, 4.0, 5.0};