All URLs in a batch share a single workspace directory. When multiple
URLs resolve to the same filename (e.g. two different domains both
serving photo.jpg), the second writeFile silently overwrites the first.
Track used filenames in a Set and append _1, _2, etc. on collision,
mirroring the existing getUniqueName pattern from batch.ts.
Accepts { urls: string[] } (1-50), fetches each URL with SSRF protection
via safeFetch, validates as image, saves to workspace, generates WebP
preview for non-browser formats, and returns results with download URLs.
Uses p-queue with concurrency 4 to parallelize fetches.
SnapOtter