tui: separator above final agent message (#4324)

Adds a separator line before the final agent message

<img width="1011" height="884" alt="Screenshot 2025-09-26 at 4 55 01 PM"
src="https://github.com/user-attachments/assets/7c91adbf-6035-4578-8b88-a6921f11bcbc"
/>

codex-rs/tui/src/bottom_pane/mod.rs

@@ -102,6 +102,10 @@ impl BottomPane {
         }
     }
 
+    pub fn status_widget(&self) -> Option<&StatusIndicatorWidget> {
+        self.status.as_ref()
+    }
+
     fn active_view(&self) -> Option<&dyn BottomPaneView> {
         self.view_stack.last().map(std::convert::AsRef::as_ref)
     }