Provisioning assigned AuthenticationProviderId and only then called
IUserManager.ChangePassword. Jellyfin dispatches that call to the provider the
user is currently assigned to, so it reached this plugin's own ChangePassword,
which refuses by design. Creating a group by typing "alice+bob" at the login
screen therefore died with NotSupportedException.
Set the placeholder password first, while the freshly created account is still
on Jellyfin's default provider, then claim it.
The new end-to-end tests wire the real provisioning, group and authentication
services together rather than mocking IProvisioningService, and cover a group
created on demand being unlocked afterwards by either member's password. With
the old ordering restored, six of them fail with the original exception.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>