NUX for gpt5.1 (#6561)

- Introducing a screen to inform users of model changes. 
- Config name is being passed to be able to reuse this component in the
future for future models

codex-rs/tui/src/chatwidget/tests.rs

@@ -1533,6 +1533,7 @@ fn single_reasoning_option_skips_selection() {
         default_reasoning_effort: ReasoningEffortConfig::High,
         supported_reasoning_efforts: &SINGLE_EFFORT,
         is_default: false,
+        recommended_upgrade_model: None,
     };
     chat.open_reasoning_popup(preset);