feat(backend): rename/group/archive/unarchive/delete/documents routes + resume read-only guard

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/app.ts

@@ -26,7 +26,7 @@ export function buildApp(config: AppConfig, deps?: BuildAppDeps): FastifyInstanc
   app.register(cors, {
     origin: true,
     credentials: true,
-    methods: ["GET", "POST", "PUT", "OPTIONS"],
+    methods: ["GET", "POST", "PUT", "DELETE", "OPTIONS"],
   });
 
   const tht = deps?.thtRunner ?? new ThtRunner({