I understand there are grey areas in what you say, but I'm not a lawyer.
"Built with GPT-6 Astra" it may mean you asked "look at the iPhone Duo page and build me the folding effect but for the MacBook", or that you ideated how it should look, what tuning options should have, discuss performance optimizations, and so on.
I do make the distinction between those two, and for the latter, which was my case, I do think there's claimable copyright.
However, I'm not interested in claiming anything regardless I would have the right or not. What I do intend, is that if somebody else builds upon this work, they do it within the OSS space as well.
If that can be legally enforced or not, well I won't stress about it.