feat: add Helm chart and release workflow

Adds a Helm chart under charts/hightower/ as an alternative to the
Flux/Kustomize deployment. Distributed via GitHub Pages (gh-pages branch).

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

charts/hightower/templates/router-configmap.yaml

@@ -0,0 +1,10 @@
+{{- if .Values.router.enabled }}
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: {{ include "hightower.router.fullname" . }}-config
+  labels:
+    {{- include "hightower.labels" . | nindent 4 }}
+data:
+  router-config.json: {{ .Values.router.config | toJson | quote }}
+{{- end }}