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/_helpers.tpl

@@ -105,6 +105,17 @@ Create the name of the secret to use for OAuth
 {{- end }}
 {{- end }}
 
+{{/*
+Create the name of the secret to use for Login Flow v2
+*/}}
+{{- define "nextcloud-mcp-server.loginFlowSecretName" -}}
+{{- if .Values.auth.loginFlow.existingSecret }}
+{{- .Values.auth.loginFlow.existingSecret }}
+{{- else }}
+{{- include "nextcloud-mcp-server.fullname" . }}-login-flow
+{{- end }}
+{{- end }}
+
 {{/*
 Create the name of the PVC to use for OAuth storage
 */}}
@@ -147,6 +158,8 @@ Checks new dataStorage.enabled OR legacy persistence configs
 true
 {{- else if and (eq .Values.auth.mode "multi-user-basic") .Values.auth.multiUserBasic.enableOfflineAccess .Values.auth.multiUserBasic.persistence.enabled -}}
 true
+{{- else if eq .Values.auth.mode "login-flow" -}}
+true
 {{- else if and (eq .Values.qdrant.mode "persistent") .Values.qdrant.localPersistence.enabled -}}
 true
 {{- else -}}