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/MainWindow.cpp

@@ -1,23 +1,24 @@
 #include "MainWindow.h"
-
 #include "ui_MainWindow.h"
 
 #include <QApplication>
-#include <QPixmap>
 #include <QScreen>
+#include <QPixmap>
 #include <QString>
+#include <QRect>
 
-MainWindow::MainWindow(QWidget* parent)
-    : QMainWindow(parent), ui(new Ui::MainWindow), pattern(QRegularExpression(R"(^[A-Za-z]+\d+$)"))
+MainWindow::MainWindow(QWidget *parent)
+    : QMainWindow(parent)
+    , ui(new Ui::MainWindow)
+    , m_pattern(QRegularExpression(R"(^[A-Za-z]+\d+$)"))
 {
     ui->setupUi(this);
 
-    // Qt6 uses UTF-8 by default; no codec needed
-    setWindowTitle(QString::fromUtf8("Qt6 Migrated Benchmark"));
-    ui->label->setText(QString::fromUtf8("Bitte Text wie Test123 eingeben."));
-    ui->iconLabel->setPixmap(QPixmap(":/icons/app.png").scaled(48, 48));
+    setWindowTitle(u"Qt6 Legacy Migration Benchmark"_s);
+
+    ui->label->setText(u"Bitte Text wie Test123 eingeben."_s);
+    ui->iconLabel->setPixmap(QPixmap(u":/icons/app.png"_s).scaled(48, 48));
 
-    // Modern function-pointer connect syntax
     connect(ui->validateButton, &QPushButton::clicked, this, &MainWindow::onValidateClicked);
     connect(ui->screenButton, &QPushButton::clicked, this, &MainWindow::onScreenInfoClicked);
 }
@@ -27,29 +28,34 @@ MainWindow::~MainWindow()
     delete ui;
 }
 
+bool MainWindow::validateInput(const QString &text) const
+{
+    return m_pattern.match(text).hasMatch();
+}
+
+QString MainWindow::getScreenInfo() const
+{
+    const QScreen *screen = QApplication::primaryScreen();
+    if (!screen) {
+        return u"Screen: unavailable"_s;
+    }
+    const QRect geometry = screen->geometry();
+    return u"Screen: %1x%2"_s.arg(geometry.width()).arg(geometry.height());
+}
+
 void MainWindow::onValidateClicked()
 {
     const QString text = ui->lineEdit->text();
 
-    if (pattern.match(text).hasMatch())
-    {
-        ui->resultLabel->setText(QString::fromUtf8("Match"));
-    }
-    else
-    {
-        ui->resultLabel->setText(QString::fromUtf8("No match"));
+    if (validateInput(text)) {
+        ui->resultLabel->setText(u"Match"_s);
+    } else {
+        ui->resultLabel->setText(u"No match"_s);
     }
 }
 
 void MainWindow::onScreenInfoClicked()
 {
-    // Qt6: Use QScreen instead of deprecated QDesktopWidget
-    const QScreen* screen = QApplication::primaryScreen();
-    if (screen)
-    {
-        const QRect screenGeometry = screen->geometry();
-        const QString info =
-            QString::fromUtf8("Screen: %1x%2").arg(screenGeometry.width()).arg(screenGeometry.height());
-        ui->resultLabel->setText(info);
-    }
+    const QString info = getScreenInfo();
+    ui->resultLabel->setText(info);
 }