function downloadVersion(versionId) {
    fetch('/api/versions/' + versionId + '/download')
        .then(function(res) {
            if (!res.ok) throw new Error('Failed to get download URL');
            return res.json();
        })
        .then(function(data) {
            window.location.href = data.download_url;
        })
        .catch(function(err) {
            showToast(err.message || 'Download failed');
        });
}