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/traefik/kustomization.yaml

@@ -0,0 +1,12 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+- namespaces.yaml
+helmCharts:
+- name: traefik
+  namespace: traefik
+  includeCRDs: true
+  releaseName: traefik
+  repo: https://traefik.github.io/charts
+  version: 39.0.7
+  valuesFile: values.yaml