v0.78.0

Added

• synapse merkle root|prove|verify ./hub.db commits the durable event log to a Merkle root: a
  single SHA-256 fingerprint of every event, so two operators — or two federated hubs — holding
  the same log derive the same root and a mismatch proves the logs differ. merkle prove SEQ
  emits an O(log n) inclusion proof for one event, and merkle verify proof.json checks that
  proof offline against a trusted root with no event store, the light-client verification a
  follower runs (--expect ROOT pins the root; --through SEQ commits only up to a sequence).
  The tree follows RFC 6962 with distinct leaf and interior-node domain-separation prefixes, so a
  leaf hash cannot be forged as an interior node. It commits what the log contains — integrity and
  inclusion — complementing the per-task reproduce digest with a log-wide, incrementally
  provable commitment. It is read-only and contacts no live hub.