tui: tweaks to dialog display (#4622)

- prefix command approval reasons with "Reason:"
- show keyboard shortcuts for some ListSelectionItems
- remove "description" lines for approval options, and make the labels
more verbose
- add a spacer line in diff display after the path

and some other minor refactors that go along with the above.

<img width="859" height="508" alt="Screenshot 2025-10-02 at 1 24 50 PM"
src="https://github.com/user-attachments/assets/4fa7ecaf-3d3a-406a-bb4d-23e30ce3e5cf"
/>

codex-rs/tui/src/diff_render.rs

@@ -64,6 +64,7 @@ impl From<DiffSummary> for Box<dyn Renderable> {
             path.push_span(" ");
             path.extend(render_line_count_summary(row.added, row.removed));
             rows.push(Box::new(path));
+            rows.push(Box::new(RtLine::from("")));
             rows.push(Box::new(row.change));
         }