When a user views a page and has reading lists enabled (with the "Save page" bookmark button), we should not query the database to get the default reading list id.
Instead the api endpoint (ApiReadingListsCreateEntry) could be updated to make the list id optional, and the default action is to save the page to the default list.
In the future, if we allow the user to use the "save pages" button to save to a non-default list, then the list id could be in user preferences.