v0.37.0 — recall query-stream for the persistent-memory layer

Added

• A recall query-stream primitive for an optional persistent-memory layer. A
  recall_log message and SynapseAgent.log_recall(...) record each lookup the
  fleet makes — the query and its outcome (returned ids, whether the answer was
  used, whether the layer abstained) — as a durable recall event. The hub
  attests the producing identity and the time (they cannot be self-reported) and
  journals the record without broadcasting it, so a downstream memory adapter can
  calibrate recall against the real query distribution from the durable log. The
  hub stays memory-agnostic: it carries the record opaquely and never indexes it.