hi friends - is there a API endpoint to "sign up" a user using the self hosted version of calcom?

It's not there yet. It is in the works. @zomars would have more information

thanks @Hariom Balhara - also do you know if there is a feature yet for an organization owner to create a 'default' calendar for org members that is locked?

I don't think such a feature exist yet.

Right now only admin users can create new users by making a POST request to /users