feat(tui) /personality (#9718)

## Summary
Adds /personality selector in the TUI, which leverages the new core
interface in #9644

Notes:
- We are doing some of our own state management for model_info loading
here, but not sure if that's ideal. open to opinions on simpler
approach, but would like to avoid blocking on a larger refactor
- Right now, the `/personality` selector just hides when the model
doesn't support it. we can update this behavior down the line

## Testing
- [x] Tested locally
- [x] Added snapshot tests

codex-rs/tui/src/bottom_pane/mod.rs

@@ -215,6 +215,11 @@ impl BottomPane {
         self.request_redraw();
     }
 
+    pub fn set_personality_command_enabled(&mut self, enabled: bool) {
+        self.composer.set_personality_command_enabled(enabled);
+        self.request_redraw();
+    }
+
     pub fn status_widget(&self) -> Option<&StatusIndicatorWidget> {
         self.status.as_ref()
     }