mount admin dashboard at /admin
rails_admin initializer
add admin boolean column to user table
seedfile creates Admin user
all devise views call devise_error_messages helper
user validations on presence of first name, last name, and email
user doesn't need email presence validation; devise handles
rails_admin initializer redirects to main_app root unless user is an admin
seeded admin user is automatically confirmed
redirect to rails_admin path if resource is an admin