Add Helm chart and chart-release workflow

charts/terdut-server/ — Helm chart for Kubernetes deployment:
  - Deployment (replicas=1, /healthz probes, TERDUT_DB_PATH=/data/terdut.db)
  - Service (ClusterIP :8080)
  - PVC (1Gi, synology-iscsi) mounted at /data
  - HTTPRoute via envoy-main gateway

.github/workflows/chart-release.yml — packages and publishes the chart to
gh-pages branch on any push to main that touches charts/; repo URL will be
https://yeniklas.github.io/terdut-server once the repo is made public

charts/terdut-server/templates/deployment.yaml

@@ -0,0 +1,48 @@
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: {{ include "terdut-server.fullname" . }}
+  labels:
+    {{- include "terdut-server.labels" . | nindent 4 }}
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      {{- include "terdut-server.selectorLabels" . | nindent 6 }}
+  template:
+    metadata:
+      labels:
+        {{- include "terdut-server.selectorLabels" . | nindent 8 }}
+    spec:
+      enableServiceLinks: false
+      containers:
+        - name: terdut-server
+          image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
+          imagePullPolicy: {{ .Values.image.pullPolicy }}
+          ports:
+            - name: http
+              containerPort: {{ .Values.service.port }}
+              protocol: TCP
+          env:
+            - name: TERDUT_ADDR
+              value: ":{{ .Values.service.port }}"
+            - name: TERDUT_DB_PATH
+              value: "/data/terdut.db"
+          volumeMounts:
+            - name: data
+              mountPath: /data
+          livenessProbe:
+            httpGet:
+              path: /healthz
+              port: http
+            initialDelaySeconds: 5
+          readinessProbe:
+            httpGet:
+              path: /healthz
+              port: http
+            initialDelaySeconds: 5
+      volumes:
+        - name: data
+          persistentVolumeClaim:
+            claimName: {{ .Release.Name }}-data