Okay, progress made.
Found another thread (Cannot find location of Aeon USB Stick) which suggested the following command:
sudo usermod -a -G dialout openhab
After rebooting, success, it can see the device!
Unfortunately, upon selecting /dev/ttyUSB0 in the Telegesis Coordinator config screen in PaperUI, it then says:
ERROR: 500 - Internal Server Error
I shall keep searching…