auth/actor_lookup_actions.ts

actor_lookup RPC handler.

Pure read — no audit, no side effects. Auth (account: 'required') + rate-limit (account-grain) enforced at the spec layer; see auth/actor_lookup_action_specs.ts for the info-leak audit.

display_name is omitted (not null) when actor.name is blank, matching the wire shape display_name? so the typed client sees an undefined rather than a sentinel string.