Add double-Escape to clear composer input in TUI

What variant of Codex are you using?

CLI

What feature would you like to see?

When composing in TUI, allow "double Esc" to clear the current input quickly:

• first Esc starts a short timeout window
• second Esc within the window clears the composer
• other keys in between cancel the action
• existing modal/popup Esc behavior remains unchanged

This is a UX/DX improvement for quickly resetting partially typed input.
Related work: I implemented this in my fork on branch Ray0907:feat/double-esc-
clear-composer.

Additional information

_No response_