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/server.yaml

@@ -42,7 +42,7 @@ spec:
               value: mg4
             # Where a phone reaches the server; the pairing QR code points here.
             - name: PUBLIC_URL
-              value: https://car.stinnesbeck.com
+              value: https://car.k8s.stinnesbeck.com
             - name: INFLUX_TOKEN
               valueFrom:
                 secretKeyRef: