UwUAuth Server 0.5.0-beta.2

SCIM finds a person an app already knows by UwUAuth's id first. When an app answers 409
to a new person, UwUAuth now looks them up by externalId before userName, and never takes
over an account there whose externalId belongs to someone else — that person is reported as
an error instead. Before, a person whose address matched someone else's account in the app
could be tied to it, and changing an address could leave a person unmanaged there, so that
disabling them never reached the app.