\section*{Statement on the use of AI}
\addcontentsline{toc}{section}{Statement on the use of AI}

The proof presented here was developed by GPT-6 Astra under the
direction of the author. The writeup was examined and edited
by Claude Fable 5.2: five independent referee passes, one for each
part of the proof, checked the arguments line by line, and a further
pass adjudicated their findings.