- Actor.permission_set_name(actor) returns role's permission set (supports nil role load).
- Actor.admin?(actor) returns true for system user or admin permission set.
- ActorIsAdmin policy check delegates to Actor.admin?/1.
Pattern match on %Mv.Accounts.User{} instead of generic actor.
Clearer intention, prevents accidental authorization bypasses.
Non-User actors are returned as-is (no-op).
SECURITY: Skip authorization for role loading to avoid circular dependency.
Actor loads their OWN role, needed for authorization itself.
Documented why this is safe.
