alice writes claim: "sky-color-836f84bc is blue" on node-1
bob writes contradicting claim: "sky-color-836f84bc is red" on node-2
  alice.id=f7dc625c-a086-4cb5-879c-8e782fa24a81 bob.id=9e7eef4b-7e73-4975-ad42-ad7adebb2e23
settle 10s for quorum fanout + contradiction indexing
charlie queries /api/v1/contradictions on node-3
  HTTP 200
  sees both memories: True; sees contradicts link: True