fix(argocd): add RBAC ConfigMap granting platform-engineer read+sync access

The platform-engineer ArgoCD account was created in argocd-cm.yaml but
no argocd-rbac-cm.yaml existed, so ArgoCD's default-deny policy blocked
all API calls with 'permission denied'. This grants the account read
access to applications, clusters, repositories, and projects, plus the
ability to trigger syncs — exactly what the platform-engineer bot needs.

argocd/argocd-rbac-cm.yaml

@@ -0,0 +1,20 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: argocd-rbac-cm
+  namespace: argocd
+  labels:
+    app.kubernetes.io/name: argocd-rbac-cm
+    app.kubernetes.io/part-of: argocd
+data:
+  # Default policy: readonly for all authenticated users
+  policy.default: role:readonly
+
+  # platform-engineer account: read all apps + trigger syncs
+  policy.csv: |
+    p, role:platform-engineer, applications, get, */*, allow
+    p, role:platform-engineer, applications, sync, */*, allow
+    p, role:platform-engineer, clusters, get, *, allow
+    p, role:platform-engineer, repositories, get, *, allow
+    p, role:platform-engineer, projects, get, *, allow
+    g, platform-engineer, role:platform-engineer