@jezmck thanks for sharing your device.
This problem is that the scripts in the project are being converted to Windows (dos) line endings on your machine before they are pushed. You were correct in spotting that the problem was due to where the 30-checktft.sh script is being executed on startup; on your device this file has the incorrect format and can’t run. I’ve deleted it for now and everything has started and I can access the web interface.
I’m not sure of the exact fix for this at the moment as I don’t have a Windows system to reproduce, but it sounds like you cloned the repo with Git rather than downloading a zip file from GitHub, in which case take a look at this: https://www.balena.io/docs/faq/troubleshooting/troubleshooting/#i-get-r-command-not-found-when-my-device-tries-to-run-scripts - it might be a case of simply changing a setting on your local Git configuration.
As I’ve left your device right now the script has been deleted so everything was able to start. I hope this helps!