v0.61.0

Added

• Added synapse verify-release, which runs declared verification commands,
  records observed stdout/stderr digests, artifact hashes, Git state, and writes
  receipt JSON for synapse release --receipt.
• Added an advisory policy engine and synapse policy-check TASK --policy <file> --receipt-json <file>, which evaluates a release receipt against a
  small JSON/TOML policy and prints deterministic pass/warn/fail/not_applicable
  decisions (required tests, strict typing evidence, owner approval, evidence
  freshness, receipt presence, known-failure acknowledgement, generated-artifact
  parity), each with the evidence it used and a next action. Advisory by default;
  --enforce exits non-zero only when an enforcement-mode policy has a failing
  rule. Pairs with verify-release receipts.