Expose model settings in app-server thread metadata (#42151)

## What changed

- Add nullable `model` and `reasoningEffort` fields to the shared app-server `Thread` object and generated schemas.
- Report current settings for loaded threads and the latest persisted settings for unloaded threads across thread read, list, start, resume, rollback, metadata update, and notification paths.
- Keep unavailable legacy or filesystem-only settings nullable, and allow metadata reads without loading a thread or dispatching queued work.

## Testing

- Cover live-setting precedence, persisted settings after restart, null legacy values, and model metadata returned by thread lifecycle operations.

GitOrigin-RevId: 22ebe8a8d1910a820d90a97730d812a00d8c1372

codex-rs/analytics/src/client_tests.rs

@@ -600,6 +600,8 @@ fn sample_thread(thread_id: &str) -> Thread {
         project_id: None,
         history_mode: Default::default(),
         model_provider: "openai".to_string(),
+        model: None,
+        reasoning_effort: None,
         created_at: 1,
         updated_at: 2,
         recency_at: Some(2),