Remove hardcoded replicas from HPA-managed deliveries StatefulSet

replicas: 4 was fighting the HPA's minReplicas: 8 on every reconcile -
GitOps tooling (Flux) reapplies the manifest on an interval, which would
keep yanking capacity back down between HPA corrections and quietly
undo the burst-headroom fix from c38a367.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

manifests/alaska/alaska.yaml

@@ -65,7 +65,9 @@ metadata:
     app.kubernetes.io/component: backend
 spec:
   serviceName: "deliveries" # Required for StatefulSet
-  replicas: 4
+  # replicas intentionally omitted - the HPA below owns this field. A
+  # hardcoded value here would fight the HPA on every GitOps reconcile,
+  # yanking replicas back down between HPA corrections.
   selector:
     matchLabels:
       app.kubernetes.io/name: deliveries