model attribution required

Commits whose content is substantially AI-generated carry Model:, and where the prompt author differs from the executor, Prompt-author-model: as well. Round reports carry an attribution block. Applied retroactively without rewriting history: PROVENANCE.md was corrected instead — and the correction included a factual error, since earlier rows named the executor as "Claude Opus 4.6" when it was Claude Opus 5 throughout.