Hide "Create a New Account” button in the Accept Invitation Screen when signup is disabled

If public sign up is disabled, the user will not be able to signup after they click the "Create a New Account" button, which is confusing.

Let's hide that button in the accept invitation screen.

Start by locating the accept invitation screen and the public sign-up setting, then trace how the screen decides which actions to show. Confirm the Create a New Account button is absent when public sign-up is disabled and remains available when sign-up is enabled.

Written by the indexing model from the issue text.