Sign out of the firm's practice system (any role)

Deletes the caller's own sealed session and their binding to the account they signed in with. The firm stays connected and every colleague stays signed in. NOTHING is sent to the practice system: the session there is the person's own and is left as it is. Until they sign in again the caller's releases answer connector.sign_in, and they are served none of that system's matters, their clients or their per-matter sets: the set of matters they were shown is deleted with the session, and their next sign-in reads it again whole. Their drafts keep the matter they name. Answers 204 whether or not there was a session. 404 while the firm has no connector, or one the firm connected once.