ci: expose non-gating Poisson tolerance failures

[xywei]

Summary

• Emit a GitHub Actions warning when --allow-fail permits a Poisson benchmark tolerance failure; emit a stderr warning locally.
• Explain that green smoke/scheduled jobs establish successful execution, not numerical acceptance.
• Add eight CLI regression cases covering pass/fail, strict/non-gating mode, local/Actions output, and preserved JSON results.

No numerical tolerances, benchmark algorithms, or workflow gating policies change. Both quick backends currently report tolerance failure under the existing acceptance criterion, which requires every sampled order to meet tolerance.

Validation

• make dev passed on Python 3.12: formatting, Ruff, mypy (74 source files), architecture, documentation, full 385-test collection (one optional skip), and all 16 cut-panel evaluations.
• Eight new CLI cases passed.
• Real quick jplus run emitted the expected Actions warning with GITHUB_ACTIONS=true.
• Section 6 polygonized parity passed all 130 metrics before this diagnostic-only change.
• Hosted push CI and pull-request CI both passed on 34bed3954eae3d626c3af72e3db0a43f014c68f7: all five jobs succeeded. Poisson smoke jobs remain intentionally non-gating for numerical acceptance.

The separate Weekly Janitor PR-creation permission failure is not addressed by this change.