fix(buildog): navigate login to sign up

[kuzeykose]

We need to navigate user to sign up if the user hasn't got any account. Right now, there is no button for that.

• Add a button on the /login page to redirect users to the /signup page if they don't have an account.
• Add a button on the /signup page to redirect users to the /login page if they already have an account.

[efesavci]

assign