feat(cluster): update K8s cluster form for new k8s_options API

Align the Kubernetes cluster create/edit page with the backend's
promotion of operator/K8s knobs out of worker_config and the removal
of gpuVendorOverrides.

- k8s_options: drop gpuVendorOverrides; add operatorImage, namespace,
  and gpuInstanceOptions (presence = GPU instances enabled, carrying an
  optional gpuInstancesAccessStaticAddress).
- Add a top-level system_default_container_registry to the cluster type
  (promoted out of worker_config on the backend).
- Group all k8s_options fields into a new top-level "K8s Deployment
  Options" collapsible section (sibling of Advanced, rendered above it),
  with namespace first followed by volume mounts, image credentials,
  node selector, operator image, and GPU instances.
- Drive the GPU instances toggle from local state instead of
  Form.useWatch (an unregistered nested path never re-rendered, leaving
  the switch unresponsive); use antd's borderless Switch and keep the
  label/switch grouped together. Namespace gains a gpustack-system
  placeholder.
- Remove the gpuVendorOverrides validation from the form and the stale
  operator_image / namespace / gpu_instances_access_static_address hints
  from the worker_config YAML template and JSON schema.
- Add-worker GPU picker: always allow multi-select for K8s clusters
  (runtime node selectors are now auto-derived), dropping the
  override-gating, cluster fetch, and single-only hint.
- Update locales (en/zh/ja/ru/tr) for the removed and added keys.

src/pages/cluster-management/config/worker-config.kubernetes.json

@@ -26,15 +26,6 @@
       "type": "string",
       "description": "Container image repository"
     },
-    "operator_image": {
-      "type": "string",
-      "description": "GPUStack operator image, format: <repo>:<tag>",
-      "examples": ["gpustack/gpustack-operator:<related version>"]
-    },
-    "gpu_instances_access_static_address": {
-      "type": "string",
-      "description": "Static address used to access GPU instances"
-    },
     "gateway_mode": {
       "type": "string",
       "description": "Gateway mode",
@@ -53,10 +44,6 @@
       "type": "string",
       "description": "Service discovery name"
     },
-    "namespace": {
-      "type": "string",
-      "description": "Kubernetes namespace"
-    },
     "huggingface_token": {
       "type": "string",
       "description": "Hugging Face access token"