[FEAT]: Support ANSI OSC52 as a "clipboard" for "Copy command"

[anku94]

Describe the need

If using Copilot CLI on remote servers over ssh, xclip/xsel etc. are rarely available. In such environments, OSC52 sequences are a simple and convenient way to access clipboards.

I tried writing a proxy script to handle xclip -in -sel clipboard (which is what Copilot CLI calls), and was only partially successful.

echo -ne "\e]52;c;$(echo -n "$data" | base64)\a"

This does not work, as the output of this command is not written to stdout for a terminal emulator to access. The following works:

data=$(cat)
echo -ne "\e]52;c;$(echo -n "$data" | base64)\a" > $OSC52_TTY

if called using

export OSC52_TTY=$(tty)
gh copilot suggest "git branch"

It is a hack, and it would be much more straightforward for Copilot CLI to emit the sequence to stdout.

Thank you!!