Hitting Ctrl+C twice should exit the TUI

Currently, ctrl+d is the keyboard shortcut to exit the TUI (like in the Python REPL). There have been numerous requests to support ctrl+c instead. Though today, ctrl+c is the way you interrupt the model (which is arguably quite intuitive since it is associated with sending SIGINT):

https://github.com/openai/codex/issues/1244.

The TypeScript CLI supports pressing Esc twice to interrupt the model, which does not seem particularly intuitive to me.

Arguably the right solution is more like the node REPL where hitting ctrl+c the first time does not quit, but prints a message telling the user that if they _really_ want to quit, they should submit ctrl+c again.