refactor: migrate from ingress-nginx to Traefik v3

Replace ingress-nginx 4.15.1 with Traefik v3 (Helm chart 39.0.7)
as the ingress controller for the local kind cluster.

- Replace k8s/nginx/ with k8s/traefik/ (Helm chart, values, namespace)
- Update setup script selectors and namespace references
- Convert nginx upstream-vhost annotations to Traefik Middleware CRDs
- Update ingressClassName from nginx to traefik

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

k8s/nginx/kustomization.yaml

@@ -1,12 +0,0 @@
-apiVersion: kustomize.config.k8s.io/v1beta1
-kind: Kustomization
-resources:
-- namespaces.yaml
-helmCharts:
-- name: ingress-nginx
-  namespace: ingress-nginx
-  includeCRDs: true
-  releaseName: ingress-nginx
-  repo: https://kubernetes.github.io/ingress-nginx
-  version: 4.15.1
-  valuesFile: https://raw.githubusercontent.com/kubernetes/ingress-nginx/main/hack/manifest-templates/provider/kind/values.yaml