feat: more role backend and admin/writer roles additions and adjustments

test/authors_backend_http_test.go

@@ -14,7 +14,7 @@ import (
 )
 
 const (
-	ownerOrAdminRefusal = "Only owners and admins can do this."
+	ownerOrAdminRefusal = apperr.MissingPermissionErrorMessage
 	sessionRefusal      = "This action needs a real session."
 )