ops(prop): pin HPA to 1 replica

Set minReplicas == maxReplicas == 1 on the `prop` HPA so the cluster
runs exactly one app pod. HPA still owns the replica count (Flux
ignores spec.replicas on the Deployment), so this is the right knob —
no need to touch deployment.yaml. Restore autoscaling by raising both
bounds together.

k8s/hpa.yaml

@@ -22,8 +22,11 @@ spec:
     apiVersion: apps/v1
     kind: Deployment
     name: prop
-  minReplicas: 2
-  maxReplicas: 5
+  # Pinned at 1 pod (min == max). HPA still owns the replica count so
+  # Flux reconcile stays out of the way; raise both bounds together to
+  # restore autoscaling.
+  minReplicas: 1
+  maxReplicas: 1
   metrics:
     - type: Resource
       resource: