[BENCH-810] Finish live-owned STT/TTS validation

[kdmelon]

Summary

• allow the exact live-owned timing-only failed-TTS shape while requiring proof from an existing dual-written observation
• keep successful TTS generated-audio validation and deterministic backfill-owned comparisons strict
• classify live conflicts into aggregate-safe categories and report bounded non-displayed provenance differences separately
• cover malformed, foreign, duplicate, ambiguous, and unexpected child data plus dry-run idempotence and frozen bounds

Testing

• ruff check on the changed production and test files
• mypy --strict on the changed production and test files
• pytest -q tests/unit/test_normalized_storage_backfill.py with the five PostgreSQL cases excluded: 63 passed, 5 deselected
• Tier 3 Sol → Luna → Sol cycle; final Sol review passed with no findings

Known limitations and rollout gates

• PostgreSQL-backed cases could not start on the local host because pg_config and pg_ctl are unavailable
• the read-only production dry run must use a complete seven-day window after the BENCH-797 deployment; September 11 UTC or later is the safe point
• this PR does not apply the backfill, deploy code, or enable normalized reads; those actions still require explicit approval

Linear: https://linear.app/coval/issue/BENCH-810/finish-live-owned-stttts-validation-for-the-seven-day-cutover

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