Fix/csv utf8 bom Improve CSV UTF-8 compatibility with Excel

[Space-FuCheng]

Summary

Prepend a UTF-8 BOM to exported CSV files so spreadsheet applications such as Microsoft Excel can reliably detect UTF-8 encoding when opening CSV files directly.

Why

Without a BOM, Excel on Windows may interpret UTF-8 CSV files using a local legacy encoding, which can cause non-ASCII text such as Chinese, Japanese, accented characters, and emoji to display incorrectly.

Change

• Write the UTF-8 BOM bytes (EF BB BF) before the CSV header.
• Leave the CSV data format unchanged.

Testing

• Built the playDebug APK successfully using the repository's Build workflow.
• Installed and ran the debug build.
• Exported CSV data containing Chinese text.
• Verified the exported file starts with EF BB BF.
• Verified the CSV opens directly in Microsoft Excel on Windows with Chinese text displayed correctly.

Note: some strict CSV consumers that do not handle UTF-8 BOMs may expose it as part of the first header field, though most modern CSV and spreadsheet tools handle it correctly.