Display pending child-thread approvals in TUI (#12767)

Summary
- propagate approval policy from parent to spawned agents and drop the
Never override so sub-agents respect the caller’s request
- refresh the pending-approval list whenever events arrive or the active
thread changes and surface the list above the composer for inactive
threads
- add widgets, helpers, and tests covering the new pending-thread
approval UI state

![Uploading Screenshot 2026-02-25 at 11.02.18.png…]()

codex-rs/tui/src/app_event.rs

@@ -51,6 +51,9 @@ pub(crate) enum AppEvent {
     /// Switch the active thread to the selected agent.
     SelectAgentThread(ThreadId),
 
+    /// Recompute the list of inactive threads that still need approval.
+    RefreshPendingThreadApprovals,
+
     /// Start a new session.
     NewSession,