QCoreApplication::quit() is not working before app.exec()

[jmlich]

According to the documentation https://doc.qt.io/qt-6/qcoreapplication.html#quit, QCoreApplication::quit() works only when app.exec() is running.

The DeviceInterface::registerDBus function is invoked within the DeviceInterface constructor, which occurs before app.exec(). As a result, the second instance of the daemon fails to register the DBus interface but does not exit immediately.

Steps to reproduce the issue:

• Try to run two instances of the daemon.
• Expected result: The second instance should exit immediately upon startup.