## Description
Spreadsheet applications such as Microsoft Excel do not auto-detect
UTF-8 encoding when opening CSV files. This causes non-ASCII characters
(Arabic, Japanese, Chinese, Korean, etc.) to appear garbled in the
exported contacts CSV.
This PR prepends the UTF-8 Byte Order Mark (`EF BB BF`) to the CSV
output in `Account::ContactsExportJob`, which signals to spreadsheet
applications that the file is UTF-8 encoded.
Fixes: #13998