feat(consul): deploy HashiCorp Consul 1.22.7 via Helm chart (5-replica cluster) (#149)

## Summary

- Deploys HashiCorp Consul 1.22.7 using Helm chart 1.9.7 with 5 server replicas
- Configuration modelled on production consul: \`datacenter=au-syd1\`, \`connect=true\`, \`raft_multiplier=10\`, HTTP on 8500, GRPC on 8502, HTTPS disabled
- 5-replica server cluster with \`bootstrapExpect=5\`
- 10Gi cephrbd-fast-delete PVC per server pod
- Gateway API: HTTPS gateway + HTTPRoute (443→consul-consul-ui:80→8500) at \`consul.k8s.syd1.au.unkin.net\`
- PodDisruptionBudget patched from \`policy/v1beta1\` to \`policy/v1\` (k8s 1.25+ compatibility)
- ArgoCD platform ApplicationSet updated to include consul overlay path
- Clients disabled (server-only deployment)
- ConnectInject disabled (can be enabled later for service mesh)

## Requires

- PR #147 (artifactapi: add hashicorp/consul to docker immutable patterns) to be merged first

## Test plan

- [ ] Sandbox tested in \`sandbox-consul\`: all 5 server pods 1/1 Running, cluster formed
- [ ] After merge: ArgoCD syncs consul namespace
- [ ] Verify \`consul.k8s.syd1.au.unkin.net\` is accessible via Gateway

Reviewed-on: #149

argocd/applicationsets/platform.yaml

@@ -15,6 +15,7 @@ spec:
       - path: apps/overlays/*/cert-manager
       - path: apps/overlays/*/certificates
       - path: apps/overlays/*/cnpg-system
+      - path: apps/overlays/*/consul
       - path: apps/overlays/*/elastic-system
       - path: apps/overlays/*/externaldns
       - path: apps/overlays/*/inteldeviceplugins-system