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

SPECS.md

@@ -7,17 +7,17 @@ what has been changed, and what is still to do.
 - Upstream: https://github.com/fatihdonmezdev/FatihsMG4 (itself a fork of malys / EVABRPUploader
   and Leon Kernan / ABRP_Uploader). Credited in the app's About dialog.
 
-## Architecture: car server at car.stinnesbeck.com
+## Architecture: car server at car.k8s.stinnesbeck.com
 
 The car sends everything to our own server. The server stores it in InfluxDB 2 and forwards live
 telemetry to ABRP, so the ABRP token lives only on the server, never in the APK. Grafana reads
 InfluxDB directly for the dashboards.
 
 ```
-car ──live telemetry───▶ car.stinnesbeck.com (Go) ──▶ ABRP  api.iternio.com/1/tlm/send
+car ──live telemetry───▶ car.k8s.stinnesbeck.com (Go) ──▶ ABRP  api.iternio.com/1/tlm/send
     ──daily chunks─────▶          │
     ──charging sessions▶          ▼
-                              InfluxDB 2 ◀── Grafana (car-grafana.stinnesbeck.com)
+                              InfluxDB 2 ◀── Grafana (car-grafana.k8s.stinnesbeck.com)
 ```
 
 - **Server:** `server/`, Go 1.26, API only — see `server/README.md` for endpoints, configuration
@@ -42,7 +42,7 @@ car ──live telemetry───▶ car.stinnesbeck.com (Go) ──▶ ABRP  ap
 - [x] Image `mg4-server:2.1.0` (with pairing) pushed to git.stinnesbeck.com (public; pinned by
       digest `sha256:e5f6e2d2…` in `k8s/kustomization.yaml`).
 - [ ] Check in `k8s/ingress.yaml`: the Traefik ingress class (placeholder `traefik-external`) and
-      Grafana's host (placeholder `car-grafana.stinnesbeck.com`).
+      Grafana's host (placeholder `car-grafana.k8s.stinnesbeck.com`).
 - [ ] First pairing and drive with 2.4.0: telemetry arrives in InfluxDB, Grafana and ABRP.
 
 ## To do