Add gitops-argo-cd agent skill

Consolidates the five cogarchhubgitops-* source skills into one skill with
scope routing: ArgoCD Applications, Copier templates, Helm values, environment
answer files, and the end-to-end resource-addition walkthrough.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

assets/example-cluster-resource/argocd/application.yaml.jinja

@@ -0,0 +1,37 @@
+{# ---------------------------------------------------------------------------
+   Template for cluster/argocd/{{ '<NNN>-<name>' if <domain>.<descriptor>_is_enabled }}/application.yaml.jinja
+
+   Replace:
+     <NNN>-<name>        three-digit band number + kebab-case descriptor (e.g. 210-eso-operator-group)
+     <target-namespace>  namespace the workload deploys into
+     <domain>            copier.yaml domain object (operators, databases, applications, …)
+     <descriptor>        this resource's key inside that domain
+
+   The parent directory name must be the Jinja2 conditional expression, and it must be
+   character-identical to the one used for the cluster/resources/ mirror.
+   --------------------------------------------------------------------------- #}
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: <NNN>-<name>
+  namespace: openshift-gitops
+  finalizers:
+    - resources-finalizer.argocd.argoproj.io
+spec:
+  project: default
+  source:
+    repoURL: {{ gitops.repo_url }}
+    targetRevision: {{ gitops.branch }}
+    path: cluster/resources/<NNN>-<name>
+    helm:
+      valueFiles:
+        - values.yaml
+  destination:
+    server: https://kubernetes.default.svc
+    namespace: <target-namespace>
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true
+    syncOptions:
+      - CreateNamespace=true