Stat Panel: Label is drawn behind sparkline

### What happened? When both sparkline and label are turned on in the stat panel, the sparkline draws over the label, making it difficult to read. <img width="420" height="200" alt="Image" src="https://github.com/user-attachments/assets/85efa436-87a0-4734-8ce9-10f3530c743c" /> ### What did you expect to happen? The label should be at a higher z-height to avoid this. ### Did this work before? No :( ### How do we reproduce it? 1. Create a stat panel where the sparkline and the label overlap ### Is the bug inside a dashboard panel? _No response_ ### Environment (with versions)? Grafana: OS: Browser: ### Grafana platform? Kubernetes ### Datasource(s)? _No response_