refactor: 全局重命名 k8s → kubernetes (前后端+路由+表名+文件)

后端:
  - pkg/k8sclient → pkg/kubernetesclient
  - models/k8s.go → models/kubernetes.go
  - handlers/k8s.go → handlers/kubernetes.go
  - K8sCluster/K8sNode/.. → KubernetesCluster/KubernetesNode/..
  - K8sHandler → KubernetesHandler
  - 路由: /k8s-clusters → /kubernetes-clusters
  - 路由: /k8s/:code/namespace/:ns/... → /kubernetes/:code/namespace/:ns/... (Kuboard风格)
  - 表前缀: container_k8s_ → container_kubernetes_

前端:
  - components/k8s/ → components/kubernetes/
  - K8sClusters → KubernetesClusters
  - K8sWorkloads → KubernetesWorkloads
  - K8sNodes → KubernetesNodes
  - k8sApi → kubernetesApi
  - 路由前缀: /k8s/ → /kubernetes/

测试验证:
✅ /kubernetes/k8s-cluster-liren/namespace/kube-system/deployments → 3 items
✅ /kubernetes/k8s-cluster-liren/namespace/kube-system/pods → 7 items
✅ /kubernetes/k8s-cluster-liren/namespace/kube-system/services → 4 items
✅ /kubernetes/k8s-cluster-liren/namespace/kube-system/configmaps → 6 items
✅ /kubernetes/k8s-cluster-liren/namespace/kube-system/secrets → 1 item
✅ /kubernetes/k8s-cluster-liren/namespaces → 4 items

frontend/src/components/dashboard/DashboardRecent.tsx

@@ -295,7 +295,7 @@ export function ServerStatusCard({ servers }: { servers: any[] }) {
 }
 
 // K8s集群状态卡片
-export function K8sClusterCard({ clusters }: { clusters: any[] }) {
+export function KubernetesClusterCard({ clusters }: { clusters: any[] }) {
   const navigate = useNavigate();
   return (
     <Card className="bg-slate-900 border-slate-800">