Move the server to car.k8s.stinnesbeck.com

The server's host is car.k8s.stinnesbeck.com, not car.stinnesbeck.com:
IngressRoute, PUBLIC_URL (so the pairing QR code points there), the
app's pre-filled server URL and hint, and the docs. Grafana's
placeholder host follows to car-grafana.k8s.stinnesbeck.com, so one
*.k8s.stinnesbeck.com default certificate covers both. App 2.4.1 for the
new default; the server image is unchanged (its URL comes from the
manifest).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QLJfZQZeAKAwSqViTmLzki

k8s/grafana.yaml

@@ -52,7 +52,7 @@ spec:
               containerPort: 3000
           env:
             - name: GF_SERVER_ROOT_URL
-              value: https://car-grafana.stinnesbeck.com
+              value: https://car-grafana.k8s.stinnesbeck.com
             - name: GF_SECURITY_ADMIN_USER
               value: admin
             - name: GF_SECURITY_ADMIN_PASSWORD