configs.hass: only allow the id.lassul.us login
Mounts an empty auth_providers list to /config/auth_providers.yaml. homeassistant: auth_providers is read only from configuration.yaml, packages can't set it, so the volume's configuration.yaml includes it once (auth_providers: !include auth_providers.yaml under homeassistant:). Without the homeassistant provider only auth_oidc remains: the welcome page redirects straight to id.lassul.us and no password form is offered.
Long-lived access tokens have no credential and are not checked against a provider, so they keep working. Refresh tokens from earlier password logins fail on the next refresh and need one id.lassul.us login. The password credentials stay in the auth store, so a revert brings the password login back.