Add clusterRef to BindTSIGKey

TSIG keys were included in every cluster's keys.conf namespace-wide. When
multiple clusters share a namespace, that leaks keys across clusters. Add
spec.clusterRef so a key can target a specific BindCluster; empty keeps
the shared (all-clusters-in-namespace) behaviour.

- api: BindTSIGKey.spec.clusterRef (optional)
- BindCluster keys.conf now includes only keys with matching or empty
  clusterRef
- regenerate CRDs + install.yaml bundle

internal/controller/bindcluster_controller.go

@@ -128,7 +128,15 @@ func (r *BindClusterReconciler) reconcileKeysSecret(ctx context.Context, c *bind
 	if err := r.List(ctx, &keys, client.InNamespace(c.Namespace)); err != nil {
 		return err
 	}
-	items := append([]bindv1alpha1.BindTSIGKey(nil), keys.Items...)
+	// Include keys scoped to this cluster (spec.clusterRef == name) and shared
+	// keys (empty clusterRef). This keeps keys from leaking across clusters that
+	// share a namespace.
+	var items []bindv1alpha1.BindTSIGKey
+	for _, k := range keys.Items {
+		if k.Spec.ClusterRef == "" || k.Spec.ClusterRef == c.Name {
+			items = append(items, k)
+		}
+	}
 	sort.Slice(items, func(i, j int) bool { return items[i].Name < items[j].Name })
 
 	var b strings.Builder