feat(git-remote-entire): surface wrong-cluster clone errors clearly

When a repo lives on a different cluster than the one in the entire:// URL, the data plane rejects the token exchange with an RFC 8693 invalid_target carrying an error_description naming the correct host. Previously this surfaced as a raw, multiply-wrapped HTTP 400 JSON blob.

Now git-remote-entire detects this case and prints an actionable message naming the correct host and the corrected git clone entire://... URL.