feat: basic image flip support

app/mainwindow.cpp

@@ -420,6 +420,10 @@ void MainWindow::contextMenuEvent(QContextMenuEvent *event)
         menu->addAction(paste);
     }
 
+    menu->addSeparator();
+
+    menu->addAction(m_am->actionHorizontalFlip);
+
     menu->addSeparator();
     menu->addAction(stayOnTopMode);
     menu->addAction(protectedMode);
@@ -554,6 +558,11 @@ void MainWindow::on_actionZoomOut_triggered()
     m_graphicsView->zoomView(0.8);
 }
 
+void MainWindow::on_actionHorizontalFlip_triggered()
+{
+    m_graphicsView->flipView();
+}
+
 void MainWindow::on_actionCopyPixmap_triggered()
 {
     QClipboard *cb = QApplication::clipboard();