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/api-serviceaccount.yaml

@@ -0,0 +1,8 @@
+{{- if .Values.api.serviceAccount.create }}
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: {{ include "hightower.serviceAccountName" . }}
+  labels:
+    {{- include "hightower.labels" . | nindent 4 }}
+{{- end }}