Soft-delete a user. Per SCIM 2.0 (RFC 7644 §3.6) this returns 204 No
Content on success. Internally the user is deactivated (active=false)
and the vendorid/role app_metadata are cleared so the user can no
longer access Tackle resources. The underlying Auth0 user record is
preserved so SSO logins can be re-authorized if the user is later
re-provisioned, and so identity providers that probe DELETE during
their connection-test lifecycle (e.g. JumpCloud) can complete
activation without permanently destroying the test user.