feat: add backup dialog when opening an existing project

sources/ui/backupdialog.h

@@ -0,0 +1,32 @@
+/*
+	Copyright 2006-2026 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech 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 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech 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 for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef BACKUPDIALOG_H
+#define BACKUPDIALOG_H
+
+#include <QDialog>
+
+class BackupDialog : public QDialog
+{
+	Q_OBJECT
+	public:
+		explicit BackupDialog(QWidget *parent = nullptr);
+		~BackupDialog() override;
+};
+
+#endif // BACKUPDIALOG_H