GET /v1/me - the principal, plus the human behind it where one is resolvable.
user_id is the usr_ id of the tenant user whose first-party dashboard session
accompanied the request (the browser attaches the session cookie alongside the console
key). It is what lets the portal offer “assign to me” against surfaces keyed on
users.id. Null - and typed that way - for a key-only caller: an API key names an
integration, not a person, and inventing one would be worse than answering none.