Did you sign any contract with the university regarding using their resources for side work unrelated to your PhD? If you didn't I would not worry too much abo

Did you sign any contract with the university regarding using their resources for side work unrelated to your PhD? If you didn't I would not worry too much about it. To get in trouble you would have to execute your idea and turn it into a business that is worth going to court or arbitration for (with very little chances of winning). Chances of that happening are so slim that you should worry about many other things first. For piece of mind you can host a virtual machine and work there. Keep in mind that usually if IT wants they can monitor every keystroke on your laptop, so there's really no privacy when working on a computer provided and managed by others.