Phase 2 of docs/plans/issue-1085-rate-limit-design.md:
- Batch import: items that fail due to vendor rate limiting are now
SKIPPED with a "re-run the import later" hint instead of FAILED, so a
transient 429 no longer pollutes failure accounting; the progress
broadcast carries a rate_limited flag.
- Batch import UI: show a one-time "rate limited — slowing down" toast
and swap the running status text while rate_limited; i18n keys synced
to all locales.
- Downloader: download_file / download_to_memory / get_response_headers
register 429 cooldowns with the RateLimitCoordinator, so subsequent
API calls queue behind a download-triggered rate-limit window.