Instrumented test driving the real NextcloudProvider over TLS: connect,
create dir, atomic upload (temp+MOVE), list+size, download+content, then the
backup guarantee — Upload-only + KEEP yields SKIP and the cloud copy is
verified still present; MIRROR yields DELETE_REMOTE and the real delete is
confirmed. Creds passed via instrumentation args (ncUrl/ncUser/ncPass), never
committed. Verified passing on a Galaxy S23 (Android 16) against live Nextcloud.
