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/base/consul/gateway.yaml

@@ -0,0 +1,51 @@
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: Gateway
+metadata:
+  name: consul
+  namespace: consul
+  labels:
+    app.kubernetes.io/name: consul
+    app.kubernetes.io/instance: consul
+    traefik.io/instance: internal
+  annotations:
+    cert-manager.io/cluster-issuer: vault-issuer
+    cert-manager.io/common-name: consul.k8s.syd1.au.unkin.net
+    cert-manager.io/private-key-size: "4096"
+    cert-manager.io/alt-names: consul.service.consul
+    external-dns.alpha.kubernetes.io/hostname: consul.k8s.syd1.au.unkin.net
+    external-dns.alpha.kubernetes.io/target: 198.18.200.4
+spec:
+  gatewayClassName: traefik-internal
+  listeners:
+    - name: http
+      port: 80
+      protocol: HTTP
+      hostname: consul.k8s.syd1.au.unkin.net
+      allowedRoutes:
+        namespaces:
+          from: Same
+    - name: https
+      port: 443
+      protocol: HTTPS
+      hostname: consul.k8s.syd1.au.unkin.net
+      allowedRoutes:
+        namespaces:
+          from: Same
+      tls:
+        mode: Terminate
+        certificateRefs:
+          - kind: Secret
+            name: consul-tls
+    - name: consul-svc
+      port: 443
+      protocol: HTTPS
+      hostname: consul.service.consul
+      allowedRoutes:
+        namespaces:
+          from: Same
+      tls:
+        mode: Terminate
+        certificateRefs:
+          - kind: Secret
+            name: consul-tls