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/secret.yaml

@@ -45,3 +45,17 @@ data:
   {{ .Values.auth.oauth.clientSecretKey }}: {{ .Values.auth.oauth.clientSecret | b64enc | quote }}
 {{- end }}
 {{- end }}
+---
+{{- if eq .Values.auth.mode "login-flow" }}
+{{- if not .Values.auth.loginFlow.existingSecret }}
+apiVersion: v1
+kind: Secret
+metadata:
+  name: {{ include "nextcloud-mcp-server.fullname" . }}-login-flow
+  labels:
+    {{- include "nextcloud-mcp-server.labels" . | nindent 4 }}
+type: Opaque
+data:
+  {{ .Values.auth.loginFlow.tokenEncryptionKeyKey }}: {{ .Values.auth.loginFlow.tokenEncryptionKey | b64enc | quote }}
+{{- end }}
+{{- end }}