improve suspend behavior (#2569)

This is a somewhat roundabout way to fix the issue that pressing ^Z
would put the shell prompt in the wrong place (overwriting some of the
status area below the composer). While I'm at it, clean up the suspend
logic and fix some suspend-while-in-alt-screen behavior too.

codex-rs/tui/src/transcript_app.rs

@@ -62,6 +62,7 @@ impl TranscriptApp {
 
     fn handle_key_event(&mut self, tui: &mut tui::Tui, key_event: KeyEvent) {
         match key_event {
+            // Ctrl+Z is handled at the App level when transcript overlay is active
             KeyEvent {
                 code: KeyCode::Char('q'),
                 kind: KeyEventKind::Press,