feat: migrate vso-system to ArgoCD (#81)

Migrate Vault Secrets Operator from Terragrunt to ArgoCD/Kustomize.
Deploys vault-secrets-operator v1.2.0 with 3 replicas, plus ClusterRole,
ClusterRoleBindings, and vault-admin ServiceAccount.

Note: static service account tokens (kubernetes.io/service-account-token)
cannot be stored in git; create manually or via Vault after deployment.

💘 Generated with Crush

Assisted-by: Claude Sonnet 4.6 via Crush <crush@charm.land>

Reviewed-on: #81

apps/base/vso-system/namespace.yaml

@@ -0,0 +1,7 @@
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  labels:
+    app.kubernetes.io/name: vso-system
+  name: vso-system