Clear composer on fork (#3445)

Fixes this

<img width="344" height="51" alt="image"
src="https://github.com/user-attachments/assets/f227d338-b044-4f8d-bf07-87499b4230d8"
/>

codex-rs/tui/src/chatwidget.rs

@@ -1316,6 +1316,11 @@ impl ChatWidget {
         self.bottom_pane.insert_str(text);
     }
 
+    /// Replace the composer content with the provided text and reset cursor.
+    pub(crate) fn set_composer_text(&mut self, text: String) {
+        self.bottom_pane.set_composer_text(text);
+    }
+
     pub(crate) fn show_esc_backtrack_hint(&mut self) {
         self.bottom_pane.show_esc_backtrack_hint();
     }