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

argocd/applicationsets/platform.yaml

@@ -11,6 +11,7 @@ spec:
       revision: HEAD
       directories:
       - path: apps/overlays/*/artifactapi
+      - path: apps/overlays/*/cattle-system
       - path: apps/overlays/*/certificates
       - path: apps/overlays/*/reflector-system
       - path: apps/overlays/*/reloader-system

argocd/projects/platform.yaml

@@ -10,6 +10,7 @@ spec:
     - https://git.unkin.net/unkin/argocd-apps
     - oci://ghcr.io/emberstack/helm-charts
     - oci://ghcr.io/woodpecker-ci/helm/woodpecker
+    - https://releases.rancher.com/server-charts/stable
   destinations:
     - namespace: '*-system'
       server: https://kubernetes.default.svc