Claim replication-status-server-derived

A claim's replication_status field is computed by the server from the accumulated annotation graph plus a per-discipline quorum (1 for formal verification, 2 for algorithms/crypto, 3 for ML and experimental sciences, 5 for behavioural/social), not read from the author-submitted CIR. A retraction annotation supersedes all other evidence; a contradiction with weight matching or exceeding supporting replications flips the status to contradicted; meeting the quorum of independent replications elevates it to replicated. Authors cannot self-certify replication. (Marked evidence=experiment deliberately: the derivation is enforced in code and covered by the test suite, but no claim in the production corpus has yet crossed a quorum, so the invariant has not been exercised by real traffic.)