Replace hardcoded domains with primary domain setting

app/services/create_account.rb

@@ -1,7 +1,7 @@
 class CreateAccount < ApplicationService
   def initialize(args)
     @username   = args[:username]
-    @domain     = args[:ou] || "kosmos.org"
+    @domain     = args[:ou] || Setting.primary_domain
     @email      = args[:email]
     @password   = args[:password]
     @invitation = args[:invitation]