Switch adguardhome/esphome/signal-gateway/zigbee2mqtt to PVC storage

Replaces raw hostPath (/srv/data/<app>) with a local-path PVC per app,
so these apps get proper PVC lifecycle semantics and can have a PVC
backup CronJob (matching what gitea already has) instead of being
unbacked host directories. local-path already lives on the same disk
these hostPaths did, so this isn't a storage-tier change.

adguardhome specifically: consolidates the previous split work/+conf/
hostPath mounts into a single PVC mounted at /opt/adguardhome (its own
default convention), since a real deployment can't run two hostPath
subtrees off one PVC.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01566weDFku8TaRC2CJUPVM1

esphome/templates/deployment.yaml

@@ -47,6 +47,5 @@ spec:
               mountPath: /config
       volumes:
         - name: config
-          hostPath:
-            path: {{ .Values.volume.hostPath }}
-            type: DirectoryOrCreate
+          persistentVolumeClaim:
+            claimName: {{ .Values.persistence.existingClaim | default (printf "%s-data" .Release.Name) }}