Surface Supabase email errors on the auth for

[amorriscode]

If the user gets any errors during sign up/sign in, we don't surface any of the errors.

For sign up, let's let the users know if the email already exists by checking the Supabase error.

For log in, if the password is incorrect, let's surface that as well.

Any other errors, we'll just say something generic like "Something went wrong, try again later."

[alicelovescake]

Done