fix container port: nginx listens on 80, not 8080

The unified image uses nginx on port 80 as the entrypoint, which
reverse-proxies to the Go backend on 127.0.0.1:8080 internally.
K8s was exposing 8080 directly, bypassing nginx entirely.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

k8s/ingress.yaml

@@ -43,4 +43,4 @@ spec:
           service:
             name: switchboard${DEPLOY_SUFFIX}
             port:
-              number: 8080
+              number: 80