this may be a dumb question but: I don’t need extra licenses for CI systems, do I? If not, can I use my login on the CI machine and stay logged in on my own machine? Or do only the CI machines need a license since they are building the deployed version?
The JUCE license applies to people, not machines. If someone has created part of a JUCE-based app, then that person requires a JUCE license if a closed source compiled binary is released.
You can be logged into the Projucer on your CI machine and your local machine simultaneously.