single control flow for both Esc and Ctrl+C (#2691)

Esc and Ctrl+C while a task is running should do the same thing. There
were some cases where pressing Esc would leave a "stuck" widget in the
history; this fixes that and cleans up the logic so there's just one
path for interrupting the task. Also clean up some subtly mishandled key
events (e.g. Ctrl+D would quit the app while an approval modal was
showing if the textarea was empty).

---------

Co-authored-by: Ahmed Ibrahim <aibrahim@openai.com>

codex-rs/tui/src/app.rs

@@ -276,22 +276,6 @@ impl App {
 
     async fn handle_key_event(&mut self, tui: &mut tui::Tui, key_event: KeyEvent) {
         match key_event {
-            KeyEvent {
-                code: KeyCode::Char('c'),
-                modifiers: crossterm::event::KeyModifiers::CONTROL,
-                kind: KeyEventKind::Press,
-                ..
-            } => {
-                self.chat_widget.on_ctrl_c();
-            }
-            KeyEvent {
-                code: KeyCode::Char('d'),
-                modifiers: crossterm::event::KeyModifiers::CONTROL,
-                kind: KeyEventKind::Press,
-                ..
-            } if self.chat_widget.composer_is_empty() => {
-                self.app_event_tx.send(AppEvent::ExitRequest);
-            }
             KeyEvent {
                 code: KeyCode::Char('t'),
                 modifiers: crossterm::event::KeyModifiers::CONTROL,