feat: show forked from session id in /status (#9330)

Summary:
- Add forked_from to SessionMeta/SessionConfiguredEvent and persist it
for forked sessions.
- Surface forked_from in /status for tui + tui2 and add snapshots.

codex-rs/tui/src/chatwidget/tests.rs

@@ -131,6 +131,7 @@ async fn resumed_initial_messages_render_history() {
     let rollout_file = NamedTempFile::new().unwrap();
     let configured = codex_core::protocol::SessionConfiguredEvent {
         session_id: conversation_id,
+        forked_from_id: None,
         model: "test-model".to_string(),
         model_provider_id: "test-provider".to_string(),
         approval_policy: AskForApproval::Never,
@@ -428,6 +429,7 @@ async fn make_chatwidget_manual(
         current_status_header: String::from("Working"),
         retry_status_header: None,
         thread_id: None,
+        forked_from: None,
         frame_requester: FrameRequester::test_dummy(),
         show_welcome_banner: true,
         queued_user_messages: VecDeque::new(),