Available midi interface refresh option after LMMS is started

### Enhancement Summary

Hi, when you connect a usb midi keyboard is not reconized. You need yo restart LMMS. Is it possible to add a scan for new devices option onder setting\Midi settings? And/or on a song track setting under MIDI/input ?

### Implementation Details / Mockup

I often load LMMS without a keyboard attached and when I want to use a keyboard I need to restart LMMS.

### Please search the issue tracker for existing feature requests before submitting your own.

- [X] I have searched all existing issues and confirmed that this is not a duplicate.

No files, tests, or entry points are named. Start by locating MIDI device initialization and the MIDI settings UI, then determine how a refresh action could be exposed after startup. Done means a USB MIDI keyboard connected after LMMS starts becomes available without restarting, with the chosen refresh location implemented.

Written by the indexing model from the issue text.