* everything is optional (username, domain and email)
* yeah, `create_account` should be mainly for signup, if a user is trying to create an account with a name that already exists I think it would be better for the user to see that the username is taken. Then they might think "oh, I already signed up, I need to log in instead". I think this is a more familiar flow. The client can easily check if that username already exists (nip-05), so they could show a "are you trying to login? click here" or something like that

I think it should publish a 31989 but not for that reason. The NIP-05 is there just to find a pubkey, then the regular flow is what's really used, so the user changing their NIP-05 to something else is irrelevant, the `connect` request is sent to the user's pubkey, not to the bunker, so the 31989 is not really necessary to locate the bunker because the discovery of the bunker itself is not necessary.