fix: reject non-finite audit confidence and skip feedback

[Pigbibi]

Scope

Audit F7: NaN/infinity confidence becomes unknown instead of NaN or fabricated 0/1. Unknown confidence cannot mutate shadow feedback. Deterministic routes and no-order controls are unchanged.

Verification

• Tests-first: 14 new cases failed on base; 5 valid/missing confidence cases passed.
• Full offline suite: 242 passed. Ruff, pip check, diff and offline sdist/wheel build passed.
• Existing uv.lock has an older Ruff selection and the frozen offline install lacked that cached wheel. Verified using complete pyproject dependency resolution offline, matching the CI install approach; no dependency/lock change.

Limits

Synthetic deterministic safety examples only; no live model evaluation, provider acquisition, deployment or order operations. Main push runs CI only.