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

apps/overlays/au-syd1/consul/kustomization.yaml

@@ -0,0 +1,16 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - ../../../base/consul
+
+helmCharts:
+  - name: consul
+    repo: https://helm.releases.hashicorp.com
+    version: "1.9.7"
+    releaseName: consul
+    namespace: consul
+    valuesFile: values.yaml
+    apiVersions:
+      - policy/v1/PodDisruptionBudget

apps/overlays/au-syd1/consul/values.yaml

@@ -0,0 +1,58 @@
+global:
+  name: consul
+  datacenter: au-syd1
+  domain: consul
+
+server:
+  image: hashicorp/consul:1.22.7
+  replicas: 5
+  bootstrapExpect: 5
+  storage: 10Gi
+  storageClass: cephrbd-fast-delete
+
+  connect: true
+
+  disruptionBudget:
+    maxUnavailable: 1
+
+  extraConfig: |
+    {
+      "disable_remote_exec": true,
+      "disable_update_check": true,
+      "performance": {
+        "raft_multiplier": 10
+      },
+      "ports": {
+        "dns": 8600,
+        "grpc": 8502,
+        "http": 8500,
+        "https": -1
+      },
+      "primary_datacenter": "au-syd1"
+    }
+
+  resources:
+    requests:
+      memory: 256Mi
+      cpu: 100m
+    limits:
+      memory: 2Gi
+      cpu: 1000m
+
+client:
+  enabled: false
+
+ui:
+  enabled: true
+  service:
+    type: ClusterIP
+
+connectInject:
+  enabled: false
+
+dns:
+  enabled: true
+  type: LoadBalancer
+  annotations: |
+    purelb.io/service-group: "common"
+    purelb.io/addresses: 198.18.200.5