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/app-server-protocol/src/protocol/v2.rs

@@ -905,6 +905,8 @@ pub struct Model {
     pub description: String,
     pub supported_reasoning_efforts: Vec<ReasoningEffortOption>,
     pub default_reasoning_effort: ReasoningEffort,
+    #[serde(default)]
+    pub supports_personality: bool,
     // Only one model should be marked as default.
     pub is_default: bool,
 }