fix: update ctrl-z to suspend tui (#2113)

- Lean on ctrl-c and esc to interrupt.
- (Only on unix.)

https://github.com/user-attachments/assets/7ce6c57f-6ee2-40c2-8cd2-b31265f16c1c

codex-rs/tui/src/chatwidget.rs

@@ -652,10 +652,6 @@ impl ChatWidget<'_> {
         }
     }
 
-    pub(crate) fn on_ctrl_z(&mut self) {
-        self.interrupt_running_task();
-    }
-
     pub(crate) fn composer_is_empty(&self) -> bool {
         self.bottom_pane.composer_is_empty()
     }