AppendAuditEntry

Append a caller-supplied event to the audit log (e.g. norsk-mgr-origin actions that don’t pass through another RPC). The daemon assigns seq
chains it. payload is opaque.

One entry in the durable, hash-chained audit log. payload is opaque (already-serialised JSON or text) so its hash stays stable regardless of consumer key ordering. prev_hash/hash form the tamper-evident chain.