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/src/exec_command.rs

@@ -1,6 +1,7 @@
 use std::path::Path;
 use std::path::PathBuf;
 
+use dirs::home_dir;
 use shlex::try_join;
 
 pub(crate) fn escape_command(command: &[String]) -> String {
@@ -27,13 +28,9 @@ where
         return None;
     }
 
-    if let Some(home_dir) = std::env::var_os("HOME").map(PathBuf::from)
-        && let Ok(rel) = path.strip_prefix(&home_dir)
-    {
-        return Some(rel.to_path_buf());
-    }
-
-    None
+    let home_dir = home_dir()?;
+    let rel = path.strip_prefix(&home_dir).ok()?;
+    Some(rel.to_path_buf())
 }
 
 #[cfg(test)]