fix(ai): migrate evidence gate to QPK v2 task service

[Pigbibi]

Completes the CryptoStrategies AI service migration started in #265.

• Remove the AIAuditBridge checkout and retired CODEX_AUDIT_SERVICE_URL / AI_GATEWAY_SERVICE_URL env from Evidence Gate.
• The old path silently passed because run_dual_review_pipeline.py no longer exists in AIAuditBridge; the gate now uses QPK task_review.review_material with three roles and fails closed (exit 3 when unavailable/pending, exit 1 unless unanimous advisory approval).
• Synthetic tests only. No secrets or deployment.