/** Download CSV (UTF-8 BOM) so Excel opens Chinese columns correctly. */
export function downloadExcelCsv(csv: string, filename: string) {
  const blob = new Blob([csv], { type: 'text/csv;charset=utf-8;' });
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = filename.endsWith('.csv') ? filename : `${filename}.csv`;
  a.click();
  URL.revokeObjectURL(url);
}