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/workspaces-pvc.yaml

@@ -0,0 +1,17 @@
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: {{ include "hightower.fullname" . }}-workspaces
+  labels:
+    {{- include "hightower.labels" . | nindent 4 }}
+  {{- if .Values.workspaces.retain }}
+  annotations:
+    helm.sh/resource-policy: keep
+  {{- end }}
+spec:
+  accessModes:
+    - {{ .Values.workspaces.accessMode }}
+  storageClassName: {{ .Values.workspaces.storageClass }}
+  resources:
+    requests:
+      storage: {{ .Values.workspaces.size }}