Fix typo in Kubernetes control plane dashboard

## Summary The Kubernetes control plane dashboard (`kubernetes/assets/dashboards/kubernetes_control_plane.json`) contains a misspelled widget title. ## Typo | Location | Current text | Suggested fix | | --- | --- | --- | | Widget title | `Nodes unealthy` | `Nodes unhealthy` | ## Impact This typo is visible to users in the shipped Kubernetes control plane dashboard template. ## Notes The other 11 dashboards under `kubernetes/assets/dashboards/` were reviewed and no additional misspellings were found. ## Proposed fix Update the widget title in `kubernetes/assets/dashboards/kubernetes_control_plane.json` to use the corrected text above.