feat: allow esc to interrupt session (#2054)

## Summary
- allow Esc to interrupt the current session when a task is running
- document Esc as an interrupt key in status indicator

## Testing
- `just fmt`
- `just fix` *(fails: E0658 `let` expressions in this position are
unstable)*
- `cargo test --all-features` *(fails: E0658 `let` expressions in this
position are unstable)*

------
https://chatgpt.com/codex/tasks/task_i_689698cf605883208f57b0317ff6a303

codex-rs/tui/src/app.rs

@@ -236,6 +236,20 @@ impl App<'_> {
                                 self.app_event_tx.send(AppEvent::ExitRequest);
                             }
                         },
+                        KeyEvent {
+                            code: KeyCode::Esc,
+                            kind: KeyEventKind::Press,
+                            ..
+                        } => match &mut self.app_state {
+                            AppState::Chat { widget } => {
+                                if !widget.on_esc() {
+                                    self.dispatch_key_event(key_event);
+                                }
+                            }
+                            AppState::Onboarding { .. } => {
+                                self.dispatch_key_event(key_event);
+                            }
+                        },
                         KeyEvent {
                             code: KeyCode::Char('z'),
                             modifiers: crossterm::event::KeyModifiers::CONTROL,