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/bottom_pane/command_popup.rs

@@ -173,6 +173,7 @@ impl CommandPopup {
                     name,
                     match_indices: indices.map(|v| v.into_iter().map(|i| i + 1).collect()),
                     is_current: false,
+                    display_shortcut: None,
                     description: Some(description),
                 }
             })