GitHub Actions cost attribution without billing access

Reconstruct GitHub Actions spend per repo / workflow / event / branch / triggering actor / job / step from run and job timestamps, when you cannot see org billing, then rank concrete CI savings with numbers. Use when: (1) someone reports "Actions usage skyrocketed" or a spending budget was raised or hit and you need to say where the minutes went, (2) the billing endpoints return 404 "needs the admin:org scope" because you are a member, not an admin, (3) `GET /repos/{o}/{r}/actions/runs/{id}/timing` returns `billable.total_ms: 0` (deprecated field - it answers 0 when it means "I cannot"), (4) jobs fail in ~4s with no steps and the annotation "The job was not started becaus…