fix(helm): add backward compatibility for legacy persistence configs

- Add helper functions to detect and use legacy persistence configs
- Legacy auth.multiUserBasic.persistence.* and qdrant.localPersistence.*
  configs continue to work but show deprecation warnings in NOTES.txt
- New dataStorage.enabled takes precedence when explicitly set
- PVC size/accessMode/storageClass values from legacy configs are honored

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

charts/nextcloud-mcp-server/templates/_helpers.tpl

@@ -138,6 +138,44 @@ Create the name of the PVC to use for /app/data storage
 {{- end }}
 {{- end }}
 
+{{/*
+Determine if data storage PVC should be enabled (backward compatible)
+Checks new dataStorage.enabled OR legacy persistence configs
+*/}}
+{{- define "nextcloud-mcp-server.dataStorageEnabled" -}}
+{{- if .Values.dataStorage.enabled -}}
+true
+{{- else if and (eq .Values.auth.mode "multi-user-basic") .Values.auth.multiUserBasic.enableOfflineAccess .Values.auth.multiUserBasic.persistence.enabled -}}
+true
+{{- else if and (eq .Values.qdrant.mode "persistent") .Values.qdrant.localPersistence.enabled -}}
+true
+{{- else -}}
+false
+{{- end -}}
+{{- end }}
+
+{{/*
+Check if legacy multi-user-basic persistence config is being used
+*/}}
+{{- define "nextcloud-mcp-server.legacyMultiUserBasicPersistence" -}}
+{{- if and (eq .Values.auth.mode "multi-user-basic") .Values.auth.multiUserBasic.enableOfflineAccess .Values.auth.multiUserBasic.persistence.enabled (not .Values.dataStorage.enabled) -}}
+true
+{{- else -}}
+false
+{{- end -}}
+{{- end }}
+
+{{/*
+Check if legacy qdrant persistence config is being used
+*/}}
+{{- define "nextcloud-mcp-server.legacyQdrantPersistence" -}}
+{{- if and (eq .Values.qdrant.mode "persistent") .Values.qdrant.localPersistence.enabled (not .Values.dataStorage.enabled) -}}
+true
+{{- else -}}
+false
+{{- end -}}
+{{- end }}
+
 {{/*
 Return the MCP server port
 */}}