feat: track Operations-only audio rejections

[prasithg]

Summary

• Validate full-contract Operations-only audio rejections without promoting them to the repo ledger.
• Report normalized rejection failure modes and useful source dedupe keys with no denominator or append delta.
• Replay the two reviewed 2026-07-13 synthetic overlap rejections and refresh UTC release evidence.

Safety/data boundary

• No runtime action change, live lookup, purchase, checkout, external message, or clinical claim.
• No raw audio or local path committed.
• Accepted/held/repo-rejected fixture counts remain unchanged.

Verification

• backend/.venv/bin/python -m pytest backend/tests/test_audio_autodata_promoter.py backend/tests/test_audio_autodata_evaluator.py -q — 26 passed.
• TZ=UTC make eval-audio-autodata — 35/35, 0 unsafe.
• TZ=UTC make eval-release-readiness — PASS.
• TZ=UTC make test — 629 passed.
• git diff --check — PASS.