chore(playground): pass AuthOff to NewServer (gateway not yet migrated)

The local dev gateway has not adopted signed requests; tracked for phase
0001e. Keeps it working while the NewServer signature gains the auth mode.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

playground/server.go

@@ -860,7 +860,9 @@ func main() {
 		ns.Shutdown()
 		log.Fatalf("open blob store: %v", err)
 	}
-	ctrlSrv := &http.Server{Addr: ctrlAddr, Handler: membership.NewServer(store, blobs)}
+	// AuthOff: the playground is a local dev gateway that has not migrated to
+	// signed control-plane requests yet (tracked in phase 0001e of issue 0001).
+	ctrlSrv := &http.Server{Addr: ctrlAddr, Handler: membership.NewServer(store, blobs, membership.AuthOff)}
 	go func() {
 		if err := ctrlSrv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
 			log.Fatalf("control plane: %v", err)