List registered hooks
List registered hooks plus the per-topic verifier bindings.
With a topic, lists only the hooks registered for that topic; without one,
lists every registered hook. The response carries the hooks under items
(with total), the per-topic verifier bindings under topic_verifiers, and
under trigger_auth how a topic’s webhook ingress door authenticates its caller —
DERIVED from the live verifier bindings just read, never stored. trigger_auth is
keyed by every topic among the LISTED hooks plus every topic currently carrying a
verifier binding (one may be bound before any hook exists on it), so under a
topic filter it is neither a subset nor a superset of the listed topics.

