Refactor auth & authz stack

[maranta1]

At the moment new accounts can only be created with LinkedIn or Google social logins. We need to be able support creating accounts using an email address.

next-auth supports magic links so this could be a good option.

https://next-auth.js.org/providers/email

LE (devpikachu): The auth & authz stack needs to be somewhat refactored and cleaned up, but more importantly the database schema needs to be cleaned up prior to a production MVP launch.