feat(helm): add login-flow auth mode to Helm chart (ADR-022)

Add Login Flow v2 as a fourth auth mode alongside basic, multi-user-basic,
and oauth. This enables multi-user deployments using Nextcloud's native
Login Flow v2 without requiring OAuth patches to user_oidc.

- Add loginFlow section to values.yaml with token encryption config
- Add login-flow env vars, args, volume mounts to deployment.yaml
- Add login-flow secret and oauth-storage PVC templates
- Add loginFlowSecretName helper, update dataStorageEnabled
- Add multi-user-basic and login-flow sections to NOTES.txt
- Add version footer and ArtifactHub changelog annotations
- Update README with 4 auth modes and docker-compose profiles

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

charts/nextcloud-mcp-server/templates/pvc.yaml

@@ -16,6 +16,21 @@ spec:
       storage: {{ .Values.auth.oauth.persistence.size }}
 {{- end }}
 ---
+{{- if eq .Values.auth.mode "login-flow" }}
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: {{ include "nextcloud-mcp-server.fullname" . }}-oauth-storage
+  labels:
+    {{- include "nextcloud-mcp-server.labels" . | nindent 4 }}
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 100Mi
+{{- end }}
+---
 {{- if and (eq (include "nextcloud-mcp-server.dataStorageEnabled" .) "true") (not .Values.dataStorage.existingClaim) }}
 {{- $legacyMultiUserBasic := eq (include "nextcloud-mcp-server.legacyMultiUserBasicPersistence" .) "true" }}
 {{- $legacyQdrant := eq (include "nextcloud-mcp-server.legacyQdrantPersistence" .) "true" }}