hi there, does anyone have any tips for modeling singleton resources? in my specific case, while we have a bunch of permissions related to specific resources in our domain (irrespective of UI), I'm finding that we want to model some permissions that are purely about whether a user can view a certain page in a UI. I'm guessing we need to actually model our UI app as a resource, but I'm not sure the best way to do that. for instance, we can have a `definition our_app` but when actually writing relationships I'm not sure what to use as the resource ID (`our_app:singleton`? `our_app:any`?). I'd love any thoughts you have on this, thanks!