Align user history message prefix width (#3467)

<img width="798" height="340" alt="image"
src="https://github.com/user-attachments/assets/fdd63f40-9c94-4e3a-bce5-2d2f333a384f"
/>

codex-rs/tui/src/lib.rs

@@ -60,6 +60,7 @@ mod status_indicator_widget;
 mod streaming;
 mod text_formatting;
 mod tui;
+mod ui_consts;
 mod user_approval_widget;
 mod version;
 mod wrapping;