Suggest SSH protocol sent username as new account name in onboarding
The SSH protocol sends a username, which is not used for authentication (but will be used as a command channel, per #7). In the onboarding flow, this username could be checked for validity/availability, and offered as a default (i.e. blank value constitutes accepting it, entering a value tries the entered value). If the name is invalid/used, a message to that effect could also be printed, so the user can know they will need to choose a different name before making a first attempt.
A simple method for reducing onboarding friction.