fix: typos in model picker (#6859)

# External (non-OpenAI) Pull Request Requirements

Before opening this Pull Request, please read the dedicated
"Contributing" markdown file or your PR may be closed:
https://github.com/openai/codex/blob/main/docs/contributing.md

If your PR conforms to our contribution guidelines, replace this text
with a detailed and high quality description of your changes.

Include a link to a bug report or enhancement request.

codex-rs/tui/src/history_cell.rs

@@ -708,6 +708,7 @@ impl SessionHeaderHistoryCell {
             ReasoningEffortConfig::Low => "low",
             ReasoningEffortConfig::Medium => "medium",
             ReasoningEffortConfig::High => "high",
+            ReasoningEffortConfig::XHigh => "extra high",
             ReasoningEffortConfig::None => "none",
         })
     }