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_symbologyimpl.cpp

@@ -71,14 +71,13 @@ TEST(SymbologyImplTest, SymbolDictionary_BasicOperations)
 // Test SymbologyImpl Qt6 QFuture continuation pattern
 TEST(SymbologyImplTest, Qt6_QFuture_Continuation_Pattern)
 {
-    // Qt6: QFuture continuation pattern
     // This test verifies the pattern used in symbol_dictionary_impl.cpp
     
     QFuture<int> future = QtConcurrent::run([]() {
         return 42;  // Simulate symbol loading count
     });
     
-    // Qt6: Use .then() for continuations
+    // QFuture::then() for continuations in Qt6
     QFuture<QString> continued = future.then([](QFuture<int> result) {
         int count = result.result();
         return QStringLiteral("Loaded %1 symbols").arg(count);
@@ -105,7 +104,6 @@ TEST(SymbologyImplTest, Qt6_API_Compatibility)
     
     EXPECT_EQ(symbolNames.size(), 3);
     
-    // Qt6: QList and QVector are identical
     QVector<QString> symbolVector = symbolNames;
     EXPECT_EQ(symbolVector.size(), 3);