Add single_ref_to_quote setting and check ref sync

app/models/concerns/has_user_settings.rb

@@ -127,6 +127,10 @@ module HasUserSettings
     settings['link_preview']
   end
 
+  def setting_single_ref_to_quote
+    settings['single_ref_to_quote']
+  end
+
   def setting_dtl_force_with_tag
     settings['dtl_force_with_tag']&.to_sym || :none
   end