Function fetch_manifest_if_newer 

pub async fn fetch_manifest_if_newer(
    current_version: &str,
) -> Result<Option<Manifest>>

Quiet variant of check_latest used by the hourly background poll. Returns the remote (version, manifest) only when strictly newer than current_version. Separate from version_check::check_latest because that one only gives back the version string; here we need the full manifest to know the per-target sha256 / size.