Add Argo CD installation manifests with Pocket ID SSO

- Downloaded upstream Argo CD install.yaml from stable branch
- Customized for basicstack.de cluster:
  - Disabled dex deployment (using Pocket ID OIDC instead)
  - Added --insecure flag to argocd-server (TLS at Traefik ingress)
  - Configured OIDC integration with auth.basicstack.de
  - Added RBAC policy mapping argo_admins group to admin role
  - Mounted OIDC client credentials from argocd-oidc-secret
- Created Traefik ingress for argo.basicstack.de with cert-manager TLS

Sealed secrets for OIDC and repository credentials already in place.
Ready for deployment per DEV-249 plan.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/argocd/argocd-ingress.yaml

@@ -0,0 +1,27 @@
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: argocd-server
+  namespace: argocd
+  annotations:
+    cert-manager.io/cluster-issuer: "letsencrypt-prod"
+    traefik.ingress.kubernetes.io/router.entrypoints: websecure
+    nginx.ingress.kubernetes.io/backend-protocol: "HTTP"
+    nginx.ingress.kubernetes.io/force-ssl-redirect: "true"
+spec:
+  ingressClassName: traefik
+  tls:
+  - hosts:
+    - argo.basicstack.de
+    secretName: argocd-server-tls
+  rules:
+  - host: argo.basicstack.de
+    http:
+      paths:
+      - path: /
+        pathType: Prefix
+        backend:
+          service:
+            name: argocd-server
+            port:
+              number: 80