DKP internal portal

Google sign-in for the staff and admin portal.

This login mirrors the `d2next` Google flow, then exchanges the Google identity token with `auth-service` so the internal portal can load the right roles and permissions for DKP staff.

Preview sample library
What staff can manage

Sample library routes, master-data registries, and future client/vendor portal boundaries

Users, roles, permissions, and resources from `auth-service`

All browser mutations stay server-side through internal route handlers