Decouple the privacy recipe from drupal_cms_content_type_base
This was raised by @thejimbirch in Slack: https://drupal.slack.com/archives/C07SKL8799Q/p1780331372899579
The privacy recipe pulls in a huge, heavy dependency (the `drupal_cms_content_type_base` recipe, which also means Canvas) so that it can...have an empty, starter privacy page. It's understandable, but it's absurdly lopsided and makes the privacy recipe less useful than it might otherwise be in the wild.
This made more sense in Drupal CMS 1.x, with its generic content types -- but it makes a lot less sense now that we have site templates _and_ a starter kit for site templates.
So, let's do this:
* Remove the default `/privacy` page from the privacy recipe. The recipe can make the assumption that a `/privacy` page exists, even if it doesn't physically ship it; this is a very reasonable convention for it to follow.
* Have the starter kit recipe supply a default, empty `/privacy` page (IOW, move that privacy page from `drupal_cms_privacy_basic` to `drupal_cms_site_template_base`). The starter kit brings in all the foundations of Drupal CMS, and it makes quite a bit more sense for it to include a basic privacy page that needs filling in.
With any luck, this will allow `drupal_cms_privacy_basic` to drop its dependency on `drupal_cms_content_type_base`!
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