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_z_proxies_integration.cpp

@@ -170,8 +170,8 @@ TEST(ZProxiesIntegration, Qt6OptionalModules)
     // Verify that optional Qt6 modules are available
     // These modules are installed via aqtinstall and apt
     
-    bool multimediaAvailable = true;  // Qt6::Multimedia
-    bool svgAvailable = true;         // Qt6::Svg
+    bool multimediaAvailable = true;  // Qt6 Multimedia module
+    bool svgAvailable = true;         // Qt6 Svg module
     
     EXPECT_TRUE(multimediaAvailable) << "Qt6::Multimedia should be available";
     EXPECT_TRUE(svgAvailable) << "Qt6::Svg should be available";