- DashboardRedisManager._Encoder: add dataclasses.asdict() for widget
  dataclasses (MetricWidgetData, ListWidgetData, TableWidgetData, etc.)
- JsonActionTokenRedisManager: use DjangoJSONEncoder so datetime/UUID/
  Decimal payloads don't crash at token creation
- DjangoSiteSettingsManager._encode_fields: use DjangoJSONEncoder for
  JSONField values instead of bare json.dumps()