Build run commit mismatch


`type`	`https://docs.frem.sh/reference/api/errors/build-run-commit-mismatch`
HTTP status	`400` Bad Request

What it means

build_run_id names a run that built a different commit than commit_sha.

Provenance that names a run and a commit which never went together is worse than none.

Send the commit the run actually built - the one the workflow checked out.

All fremforge API errors are RFC 9457 problem+json:

{
  "type": "https://docs.frem.sh/reference/api/errors/build-run-commit-mismatch",
  "title": "Bad Request",
  "status": 400,
  "detail": "..."
}

Branch on type, not on title or detail - those are human-readable and may be reworded.