The previous PNG-file fix got past URI loading but System.Drawing.Icon
needs ICO format, not raw PNG. Build a minimal ICO header (Vista+
PNG-in-ICO format) around the rendered PNG bytes and write that to
%TEMP%. H.NotifyIcon loads the file via URI, hands the bytes to
new Icon(stream), and the ICO parser accepts the embedded PNG entry.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>