feat: gate GPU Service on Kubernetes cluster availability

GPU Service today only schedules on Kubernetes clusters; Docker / cloud
clusters can't host the CRDs. Without any awareness of that, Org
members whose Org has no K8s cluster (and no cluster_access grant on
one) saw a menu they couldn't use and a form that bottomed out with
backend errors.

Two changes lock the UX down:

- Boot probes the caller's cluster list once and stashes
  hasKubernetesCluster in initialState. A new canSeeGpuService
  predicate gates the menu — admins and Org owners always see it
  (they can add the cluster); everyone else only sees it when a
  reachable K8s cluster actually exists.

- The instances page filters its own cluster list to Kubernetes
  before deciding what to show. With nothing reachable we render the
  Deployments-style 'No clusters available. Add a Kubernetes cluster
  to get started.' empty state and hide the create-instance CTA;
  admins and Org owners additionally get the 'Add cluster' button
  that jumps to cluster management.

src/locales/zh-CN/no-result.ts

@@ -35,6 +35,8 @@ export default {
   'noresult.catalog.subTitle': '尚未配置任何模型。',
   'noresult.catalog.nofound': '未找到匹配的模型',
   'noresult.resources.cluster': '暂无可用集群，请添加集群以开始使用。',
+  'noresult.resources.k8sCluster':
+    '暂无可用集群，请添加 Kubernetes 集群以开始使用。',
   'noresult.resources.worker': '暂无可用节点，请添加节点以开始使用。',
   'noresult.resources.gotocluster': '创建您的第一个集群',
   'noresult.resources.gotoworker': '添加节点',