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

features/image_variants_cache.qa.md

@@ -1,5 +1,7 @@
 # QA procedure: image_variants_cache
 
+> Superseded in part by roles_permissions_enforcement: the owner and admin 403 clauses now answer 403 "missing_permission" with the header X-Missing-Permission, decided by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.
+
 Two parts: Go for the API and tracking, Vitest for the Cache screen. No live server, no real SQLite file, no real SMTP, no `time.Sleep` (use an injected clock and manual flushes).
 
 ## Go (package `test`, black-box)