[Bug] Admin token - general issues

[hrabalvojta]

1. Admin token is enabled by default with a known value.
   values.yaml sets adminToken.value to a fixed Argon2 hash, and _podSpec.tpl always injects ADMIN_TOKEN when .Values.adminToken is non-nil. This means a fresh install enables the admin page with a token derived from a known example value. That’s a security risk.

2. adminToken=null can break rendering.
   The README suggests --set adminToken=null to disable the admin token, but secrets.yaml still does b64enc on .Values.adminToken.value. If adminToken is null, that can error during template render.