fix(tier4): prove self-quorum settlement blocker

[scarmani]

Summary

• teach settle_tier4_pr.py to fetch a diagnostic review-queue merge-packet --ignore-own-quorum-check packet when the only required-check failure is aragora-merge-quorum
• treat that self-check failure as ignorable only when the diagnostic packet proves exact head, Tier 4 human preapproval, grok + openai counted model families, dogfood evidence, no unresolved dissent, and no owner/mailbox blocker fields
• keep non-quorum failures, missing model quorum, unresolved dissent, head drift, draft state, merge conflicts, and missing settlement artifacts fail-closed

Validation

• python3 -m pytest tests/scripts/test_settle_tier4_pr.py -> 97 passed
• pre-commit run --files scripts/settle_tier4_pr.py tests/scripts/test_settle_tier4_pr.py -> passed
• Dogfood read-only: python3 scripts/settle_tier4_pr.py --check --pr 8472 --head ff27386c0f92b1099b8f01028c47fc026fdd3385 --trusted-operator-login scarmani --json now reports self_quorum_missing_settlement_proven=true and leaves only missing aragora/human-settlement status as blocker

Draft only. Do not merge until quorum/evidence and settlement gates complete.