We had client-side notification stacking in the tray since launch, but now we want to stack notifications in the notifications page, in API responses and in email bundles.
turbo-rails 2.0.21 changed `capture_turbo_stream_broadcasts` to only
return broadcasts produced within the block, matching its documented
behavior (see hotwired/turbo-rails#736).
Since `broadcast_unread` uses `broadcast_prepend_later_to` (async via
job), we need to wrap the call in `perform_enqueued_jobs` so the
broadcast actually happens within the assertion block.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>