feat: migrate cattle-system (Rancher) from Terraform to ArgoCD

- Add cattle-system base ArgoCD application with namespace, Vault integration, and ingress
- Create cattle-system overlay for au-syd1 with Rancher Helm chart configuration
- Update platform ApplicationSet to include cattle-system deployment
- Update platform project to include Rancher Helm repository as source
- Configure Rancher v2.13.1 with HA, TLS, audit logging, and bootstrap secret from Vault
- Maintain one-to-one migration from Terraform configuration

apps/base/cattle-system/vaultstaticsecret.yaml

@@ -0,0 +1,15 @@
+---
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultStaticSecret
+metadata:
+  name: rancher-bootstrap-secret
+  namespace: cattle-system
+spec:
+  vaultAuthRef: rancher
+  mount: kv
+  type: kv-v2
+  path: service/kubernetes/au/syd1/rancher/bootstrap-password
+  refreshAfter: 5m
+  destination:
+    name: rancher-bootstrap-secret
+    create: true