feat: update splash (#3631)

- Update splash styling.
- Add center truncation for long paths.
  (Uses new `center_truncate_path` utility.)
- Update the suggested commands.


## New splash
<img width="560" height="326" alt="image"
src="https://github.com/user-attachments/assets/b80d7075-f376-4019-a464-b96a78b0676d"
/>

## Example with truncation:
<img width="524" height="317" alt="image"
src="https://github.com/user-attachments/assets/b023c5cc-0bf0-4d21-9b98-bfea85546eda"
/>

codex-rs/tui/Cargo.toml

@@ -43,6 +43,7 @@ crossterm = { version = "0.28.1", features = [
     "bracketed-paste",
     "event-stream",
 ] }
+dirs = "6"
 diffy = "0.4.2"
 image = { version = "^0.25.8", default-features = false, features = [
     "jpeg",