feat: new action for fit long image

app/mainwindow.h

@@ -93,6 +93,7 @@ private slots:
     void on_actionHorizontalFlip_triggered();
     void on_actionFitInView_triggered();
     void on_actionFitByWidth_triggered();
+    void on_actionFitLongImage_triggered();
     void on_actionCopyPixmap_triggered();
     void on_actionCopyFilePath_triggered();
     void on_actionPaste_triggered();