#13126 RiaLogging: Extract errorInMessageBox to RiuMessageDialog

Move the QMessageBox-displaying helper out of the logging utility into a
dedicated UI class. RiaLogging.h no longer pulls QMessageBox/QWidget into
the ~270 files that include it. Behavior is preserved: showError displays
the dialog when running interactively (and not under regression tests),
then forwards the text to RiaLogging::error.

ApplicationLibCode/UserInterface/RiuMessageDialog.cpp

@@ -0,0 +1,44 @@
+/////////////////////////////////////////////////////////////////////////////////
+//
+//  Copyright (C) 2026-     Equinor ASA
+//
+//  ResInsight is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  ResInsight is distributed in the hope that it will be useful, but WITHOUT ANY
+//  WARRANTY; without even the implied warranty of MERCHANTABILITY or
+//  FITNESS FOR A PARTICULAR PURPOSE.
+//
+//  See the GNU General Public License at <http://www.gnu.org/licenses/gpl.html>
+//  for more details.
+//
+/////////////////////////////////////////////////////////////////////////////////
+
+#include "RiuMessageDialog.h"
+
+#include "RiaGuiApplication.h"
+#include "RiaLogging.h"
+#include "RiaRegressionTestRunner.h"
+
+#include <QMessageBox>
+
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+void RiuMessageDialog::showError( QWidget* parent, const QString& title, const QString& text )
+{
+    if ( RiaGuiApplication::isRunning() && !RiaRegressionTestRunner::instance()->isRunningRegressionTests() )
+    {
+        if ( parent == nullptr )
+        {
+            parent = RiaGuiApplication::widgetToUseAsParent();
+        }
+        QMessageBox dlg( QMessageBox::Critical, title, text, QMessageBox::Ok, parent );
+        dlg.setWindowFlags( dlg.windowFlags() | Qt::WindowStaysOnTopHint );
+        dlg.exec();
+    }
+
+    RiaLogging::error( text );
+}