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/README.md

@@ -0,0 +1,27 @@
+# Argo CD Application
+
+Apply the Application:
+
+```bash
+kubectl apply -f gitops/argocd/application.yaml
+```
+
+## Migrating from `spec.source` to `spec.sources`
+
+If the `onelab` Application was created **before** the observability stack, the live object may still have **`spec.source`** only. A plain `kubectl apply` of the new manifest often **does not remove** `spec.source`, so Argo never reconciles the second chart (Loki/Promtail/Grafana).
+
+**Check:**
+
+```bash
+kubectl get application onelab -n argocd -o jsonpath='{.spec.source}{"\n"}{.spec.sources}{"\n"}'
+```
+
+If `source` is set and `sources` is empty, patch once:
+
+```bash
+kubectl patch application onelab -n argocd --type json --patch-file gitops/argocd/jsonpatch-multisource.json
+```
+
+Then sync the app in Argo (or wait for auto-sync).
+
+Adjust `repoURL` in `jsonpatch-multisource.json` if your remote differs.