docs(reflow/integrate): show user_phase in the SSE integration example
The progress-streaming recipe destructured display_name. Update
the example to destructure user_phase too and add a two-line
comment explaining which field to drive UI off (user_phase is
the stable contract; display_name / step_name are for richer
human-readable output).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>