Persist multi-agent runtime metadata (#25721)

Stack split from #25708. Original PR intentionally left open. This
second PR persists multi-agent runtime metadata through thread creation,
rollout recording, and thread storage.

codex-rs/thread-store/src/local/create_thread.rs

@@ -35,7 +35,8 @@ pub(super) async fn create_thread(
             params.thread_source,
             params.base_instructions,
             params.dynamic_tools,
-        ),
+        )
+        .with_multi_agent_version(params.multi_agent_version),
     )
     .await
     .map_err(|err| ThreadStoreError::Internal {