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/ingress.yaml

@@ -0,0 +1,29 @@
+---
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: rancher
+  namespace: cattle-system
+  annotations:
+    cert-manager.io/cluster-issuer: vault-issuer
+    cert-manager.io/common-name: rancher.k8s.syd1.au.unkin.net
+    cert-manager.io/private-key-size: "4096"
+    external-dns.alpha.kubernetes.io/hostname: rancher.k8s.syd1.au.unkin.net
+    external-dns.alpha.kubernetes.io/target: "198.18.200.0"
+spec:
+  ingressClassName: nginx
+  tls:
+    - hosts:
+        - rancher.k8s.syd1.au.unkin.net
+      secretName: rancher-tls
+  rules:
+    - host: rancher.k8s.syd1.au.unkin.net
+      http:
+        paths:
+          - path: /
+            pathType: Prefix
+            backend:
+              service:
+                name: rancher
+                port:
+                  number: 80