Docs Bisect: find the release that broke a quickstart step

firstrun bisect replays only the steps a failing step needs, in a fresh container per probe, with the package pinned through PIP_CONSTRAINT. It binary-searches the PyPI releases the container's Python can install and saves bisect.json after every probe. No model call, so a probe costs nothing but Docker time. Live on the dbt guide: jafgen --years works on 0.3.1 (2023-01-17) and fails on 0.4.6 (2024-04-07), 5 probes.