fix: GECOS subfield trimming and trailing backslash handling (v0.3.1)

display_name() now returns only the first GECOS subfield (before comma)
instead of the full GECOS string with room numbers and phone extensions.

split_shell_words() returns None for trailing backslashes instead of
silently ignoring them.

src/users.rs

@@ -30,12 +30,12 @@ pub struct User {
 }
 
 impl User {
-    /// Return the display name (GECOS if available, otherwise username).
+    /// Return the display name (first GECOS subfield if available, otherwise username).
     pub fn display_name(&self) -> &str {
         if self.gecos.is_empty() {
             &self.username
         } else {
-            &self.gecos
+            self.gecos.split(',').next().unwrap_or(&self.username)
         }
     }
 }
@@ -150,6 +150,17 @@ mod tests {
         assert_eq!(users[0].home, PathBuf::from("/home/testuser"));
     }
 
+    #[test]
+    fn gecos_subfield_trimmed() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = make_passwd(
+            dir.path(),
+            "testuser:x:1000:1000:Test User,Room 123,555-1234:/home/testuser:/bin/bash\n",
+        );
+        let users = get_users(Some(&path));
+        assert_eq!(users[0].display_name(), "Test User");
+    }
+
     #[test]
     fn skip_system_users() {
         let dir = tempfile::tempdir().unwrap();