feat: Add LCOV coverage support for Jenkins CI

- Add ENABLE_COVERAGE CMake option with gcov flags
- Create collect-coverage.sh script for LCOV workflow
- Add Qt6 test files with QTest framework
- Update Jenkinsfile with Coverage stage (main/master/coverage.*)
- Update CI Docker image with lcov and genhtml packages
- Add .gitignore entries for coverage artifacts
- Add COVERAGE.md documentation

Coverage workflow:
1. Configure with -DENABLE_COVERAGE=ON
2. Build and run tests to generate .gcda/.gcno files
3. Collect coverage with lcov
4. Filter out Qt/system libraries
5. Generate HTML report and lcov.info for Jenkins

Jenkins publishes coverage/lcov.info using Coverage Plugin.
Coverage stage only runs on protected branches.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Entire-Checkpoint: 7783c7698334

qt6-after/qt6-migrated-benchmark/tests/test_main.cpp

@@ -0,0 +1,52 @@
+#include <QtTest/QtTest>
+
+class TestMainWindow : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void testValidateInputValid();
+    void testValidateInputInvalid();
+    void testValidateInputEmpty();
+    void testValidateInputMixedCase();
+};
+
+void TestMainWindow::testValidateInputValid()
+{
+    // Test valid input patterns
+    QRegularExpression pattern(R"(^[A-Za-z]+\d+$)");
+    
+    QVERIFY(pattern.match("Test123").hasMatch());
+    QVERIFY(pattern.match("abc456").hasMatch());
+    QVERIFY(pattern.match("ABC789").hasMatch());
+}
+
+void TestMainWindow::testValidateInputInvalid()
+{
+    // Test invalid input patterns
+    QRegularExpression pattern(R"(^[A-Za-z]+\d+$)");
+    
+    QVERIFY(!pattern.match("123Test").hasMatch());
+    QVERIFY(!pattern.match("Test").hasMatch());
+    QVERIFY(!pattern.match("123").hasMatch());
+    QVERIFY(!pattern.match("Test123ABC").hasMatch());
+    QVERIFY(!pattern.match("Test-123").hasMatch());
+}
+
+void TestMainWindow::testValidateInputEmpty()
+{
+    QRegularExpression pattern(R"(^[A-Za-z]+\d+$)");
+    QVERIFY(!pattern.match("").hasMatch());
+}
+
+void TestMainWindow::testValidateInputMixedCase()
+{
+    QRegularExpression pattern(R"(^[A-Za-z]+\d+$)");
+    
+    QVERIFY(pattern.match("TeSt123").hasMatch());
+    QVERIFY(pattern.match("aBcDeF999").hasMatch());
+}
+
+QTEST_MAIN(TestMainWindow)
+
+#include "test_main.moc"