Preview an invitation

Requires a dashboard token. No selected membership is required. Returns the organization name, role, expiry, whether the signed-in email matches the invitation, and whether this user already accepted it. The response never includes the token. It never includes the invited address, including when the emails differ. Expired, revoked, used by someone else, unknown tokens, and an invitation whose accepting user no longer has a membership all return not_found with the same error. The user who already accepted and still has a membership receives this preview with already_accepted true, including after expiry. Any other caller still receives not_found, so the used state is not disclosed to them. An organization pending deletion returns the same error as acceptance. The dashboard user request limiter applies per user.