Classify streaming rate-limit errors (#40931)

## What changed

- Classify `response.failed` events with the `rate_limit_exceeded` code as a distinct retryable error while preserving any parsed retry delay.
- Expose the error as `rateLimitExceeded` through the core protocol and app-server schemas after stream retries are exhausted.
- Preserve the upstream message for TUI display while keeping it out of telemetry summaries.

## Testing

- Cover SSE classification, retry metadata, protocol conversion and serialization, exhausted stream retries, telemetry redaction, and TUI rendering.

GitOrigin-RevId: 02dab4d3477dcd7653a58c49c4bd38687a616579