Fix Open WebUI storage and model detection

- Change emptyDir to persistent volume (open-webui-data PVC)
  Fixes data loss on pod restart (admin user disappears)

- Add ENABLE_OLLAMA_API=false
  Disable broken Ollama endpoint probing
  vLLM uses OpenAI-compatible API, not Ollama

- Create pvc.yaml for persistent data storage
  10Gi NFS-backed storage via nfs-emporium StorageClass

cluster/applications/open-webui/pvc.yaml

@@ -0,0 +1,14 @@
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: open-webui-data
+  namespace: open-webui
+  labels:
+    app.kubernetes.io/name: open-webui
+    app.kubernetes.io/component: data
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 10Gi