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

features/media_purge.qa.md

@@ -1,5 +1,7 @@
 # QA procedure: media_purge
 
+> Superseded in part by roles_permissions_enforcement: the owner and admin 403 clauses now answer 403 "missing_permission" with the header X-Missing-Permission, decided by the caller's role permissions. An Admin can now invite and write sites, and a role without the needed permission is refused on routes that were open to every verified user.
+
 Package: `test` (black-box). New files `test/media_purge_http_test.go` and `test/media_purge_test.go` (use case level). Fake type names must be unique in the package. Go only: no SPA, no scheduler, no env var.
 
 ## Setup shared by every case