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/tui2/src/chatwidget.rs

@@ -383,6 +383,7 @@ pub(crate) struct ChatWidget {
     // Previous status header to restore after a transient stream retry.
     retry_status_header: Option<String>,
     conversation_id: Option<ThreadId>,
+    forked_from: Option<ThreadId>,
     frame_requester: FrameRequester,
     // Whether to include the initial welcome banner on session configured
     show_welcome_banner: bool,
@@ -522,6 +523,7 @@ impl ChatWidget {
             .set_history_metadata(event.history_log_id, event.history_entry_count);
         self.set_skills(None);
         self.conversation_id = Some(event.session_id);
+        self.forked_from = event.forked_from_id;
         self.current_rollout_path = Some(event.rollout_path.clone());
         let initial_messages = event.initial_messages.clone();
         let model_for_header = event.model.clone();
@@ -1502,6 +1504,7 @@ impl ChatWidget {
             current_status_header: String::from("Working"),
             retry_status_header: None,
             conversation_id: None,
+            forked_from: None,
             queued_user_messages: VecDeque::new(),
             show_welcome_banner: is_first_run,
             suppress_session_configured_redraw: false,
@@ -1598,6 +1601,7 @@ impl ChatWidget {
             current_status_header: String::from("Working"),
             retry_status_header: None,
             conversation_id: None,
+            forked_from: None,
             queued_user_messages: VecDeque::new(),
             show_welcome_banner: false,
             suppress_session_configured_redraw: true,
@@ -2400,6 +2404,7 @@ impl ChatWidget {
             token_info,
             total_usage,
             &self.conversation_id,
+            self.forked_from,
             self.rate_limit_snapshot.as_ref(),
             self.plan_type,
             Local::now(),