Resume a deferred account creation parked at the register form

Completes a deferred account creation that was parked when an existing user submitted the register form while logged out, then signed in or reset their password. The parked names are unauthenticated register-form input, so the SPA first fetches them (GET accounts/resume) and calls this only after the signed-in owner explicitly confirms — never silently on sign-in. Guarded by UserJwtGuard and rate-limited to 10 per hour; the parked intent is claimed delete-first so a retried or concurrent call cannot double-create. Returns 201 with an access token bound to the new Account's first Application and sets the refresh and session-marker cookies, or 404 when there is no pending intent to resume.