[pagex] implement visibility flags

[voidcannon] migrate to visibility flags

content/authors/placeholder.pagex.js

@@ -1,7 +1,10 @@
-import {VoidcannonContentType} from "voidcannon";
+import {VoidcannonContentType, VoidcannonVisibilityFlags} from "voidcannon";
 
 export default {
     type: VoidcannonContentType.AUTHOR,
     id: "placeholder",
     name: "Placeholder Author",
+    visibility_flags: [
+        VoidcannonVisibilityFlags.HIDDEN_IN_SITEMAP,
+    ],
 }