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-service.yaml

@@ -0,0 +1,13 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: {{ include "hightower.api.fullname" . }}
+  labels:
+    {{- include "hightower.labels" . | nindent 4 }}
+spec:
+  selector:
+    {{- include "hightower.api.selectorLabels" . | nindent 4 }}
+  ports:
+    - name: http
+      port: {{ .Values.api.port }}
+      targetPort: {{ .Values.api.port }}