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/ingress.yaml

@@ -14,7 +14,7 @@ spec:
     - websecure
   routes:
     - kind: Rule
-      match: Host(`car.stinnesbeck.com`)
+      match: Host(`car.k8s.stinnesbeck.com`)
       services:
         - kind: Service
           name: mg4-server
@@ -35,7 +35,7 @@ spec:
   routes:
     - kind: Rule
       # CHECK: placeholder host. It must be covered by Traefik's default certificate.
-      match: Host(`car-grafana.stinnesbeck.com`)
+      match: Host(`car-grafana.k8s.stinnesbeck.com`)
       services:
         - kind: Service
           name: grafana