Pin lightning==2.6.1 to avoid compromised 2.6.2/2.6.3

[imbgar-roboflow]

Summary

• Pin lightning to ==2.6.1 (was >=2.4.0) so a fresh install does not resolve to the malicious wheels on PyPI.

Why

Lightning AI advisory GHSA-w37p-236h-pfx3 (published 2026-04-30) confirms that lightning / pytorch-lightning 2.6.2 and 2.6.3 on PyPI were compromised. The wheels include a hidden _runtime/ directory with a start.py downloader and an ~11 MB obfuscated router_runtime.js payload that auto-executes on import lightning, harvests credentials (GitHub/npm/PyPI tokens, cloud creds, env vars, SSH keys), and attempts to commit encoded data back to victim repos. See Socket's writeup: https://socket.dev/blog/lightning-pypi-package-compromised.

2.6.1 (published 2026-01-30) is the last known clean release. The current spec lightning>=2.4.0 is unbounded and would resolve to 2.6.3 on a fresh install — this PR forces resolvers to skip the malicious versions until upstream ships a clean replacement.

Notes

• Hard pin is intentionally narrow until Lightning AI publishes a confirmed-clean 2.6.4+. Once that lands we can relax to a >= range again.
• maestro has no lockfile, so no uv lock / poetry lock regeneration is needed — the pyproject.toml change is sufficient.

Test plan

• Confirm pip install -e . still resolves successfully
• Confirm CI passes

[CLAassistant]

All committers have signed the CLA.