Give demo app a real Longhorn-backed PVC

apps/demo/deployment.yaml

@@ -32,7 +32,15 @@ spec:
             # Mounts the ConfigMap's index.html over nginx's default page.
             - name: page
               mountPath: /usr/share/nginx/html
+            # Real, replicated storage from apps/demo/pvc.yaml — a harmless
+            # subdirectory nginx doesn't otherwise use, proving a Longhorn
+            # volume can actually be attached and written to.
+            - name: data
+              mountPath: /usr/share/nginx/html/data
       volumes:
         - name: page
           configMap:
             name: demo-page
+        - name: data
+          persistentVolumeClaim:
+            claimName: demo-data

apps/demo/pvc.yaml

@@ -0,0 +1,16 @@
+# A hands-on check that Longhorn actually works (see docs/06-longhorn.md).
+# No storageClassName is set, so Kubernetes uses whichever StorageClass is
+# marked default — Longhorn's own chart marks itself default, so this PVC
+# gets real, replicated storage on the two Proxmox workers without naming
+# Longhorn here explicitly.
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: demo-data
+  namespace: demo
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 2Gi