## 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
