fix(argocd): multisource patch doc, Ingress grafana-onelab

- Root cause: live Application kept spec.source; Argo ignored observability chart
- Add jsonpatch-multisource.json + argocd/README.md migration steps
- Grafana: disable subchart ingress; add templates/ingress-grafana-onelab.yaml

Made-with: Cursor

gitops/argocd/application.yaml

@@ -1,5 +1,8 @@
 # Syncs OneLab app + observability (Loki/Promtail/Grafana) into namespace onelab.
 # Requires Argo CD 2.6+ (spec.sources). Ensure repoURL matches your remote.
+#
+# If you already had this Application with spec.source only, kubectl apply may not drop
+# source — see README.md in this folder and jsonpatch-multisource.json.
 apiVersion: argoproj.io/v1alpha1
 kind: Application
 metadata: