feat: interrupt running task on ctrl-z (#1880)

- Arguably a bugfix as previously CTRL-Z didn't do anything.
- Only in TUI mode for now. This may make sense in other modes... to be
researched.
- The TUI runs the terminal in raw mode and the signals arrive as key
events, so we handle CTRL-Z as a key event just like CTRL-C.
- Not adding UI for it as a composer redesign is coming, and we can just
add it then.
- We should follow with CTRL-Z a second time doing the native terminal
action.

codex-rs/tui/src/app.rs

@@ -238,6 +238,16 @@ impl App<'_> {
                                 }
                             }
                         }
+                        KeyEvent {
+                            code: KeyCode::Char('z'),
+                            modifiers: crossterm::event::KeyModifiers::CONTROL,
+                            kind: KeyEventKind::Press,
+                            ..
+                        } => {
+                            if let AppState::Chat { widget } = &mut self.app_state {
+                                widget.on_ctrl_z();
+                            }
+                        }
                         KeyEvent {
                             code: KeyCode::Char('d'),
                             modifiers: crossterm::event::KeyModifiers::CONTROL,