Show estimated thread usage in /status (#38281)

## What changed

- Extend `account/usage/read` with an optional `threadId` request and a
  backward-compatible `threadUsage` response containing estimated credits,
  optional USD cost, and model, reasoning, speed, and token breakdowns.
- Fetch thread usage for eligible Business and Enterprise plans when `/status`
  is opened, then update the rendered status card asynchronously.
- Preserve terminal scrollback when replacing a visible status-card tail, and
  append a refreshed card when the original tail can no longer be updated.

## Testing

- Add app-server coverage for authentication, canonical thread IDs,
  unavailable billing routes, and malformed IDs.
- Add TUI coverage for usage formatting, stale responses, retries, history
  updates, terminal reflow, and scrollback preservation.

GitOrigin-RevId: 49300914b3fba917c0f08e8595363e04e5ba6d37

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

@@ -246,6 +246,7 @@ impl ChatWidget {
             next_status_line_workspace_headline_request_id: 0,
             status_line_workspace_headline_last_requested_at: None,
             status_line_workspace_messages_disabled: false,
+            thread_usage: thread_usage::ThreadUsageState::default(),
             current_goal_status_indicator: None,
             current_goal_status: None,
             external_editor_state: ExternalEditorState::Closed,