Gate realtime audio interruption logic to v2 (#14984)

- thread the realtime version into conversation start and app-server
notifications
- keep playback-aware mic gating and playback interruption behavior on
v2 only, leaving v1 on the legacy path

codex-rs/app-server/src/bespoke_event_handling.rs

@@ -338,6 +338,7 @@ pub(crate) async fn apply_bespoke_event_handling(
                 let notification = ThreadRealtimeStartedNotification {
                     thread_id: conversation_id.to_string(),
                     session_id: event.session_id,
+                    version: event.version,
                 };
                 outgoing
                     .send_server_notification(ServerNotification::ThreadRealtimeStarted(