Sign preview URLs for a page of assets

Signs URLs for the preview renditions (WebPs at most 400 px wide) of up to 100 of your assets in one call, each valid for 15 minutes (ttlSeconds), and reports each asset's ingest status alongside. IDs that are not yours are left out rather than reported. A read that is a POST only because a page of ids does not fit a query string, so it takes no Idempotency-Key — a replay would hand back stale signatures.

USE THIS WHEN:

• Painting thumbnails for a listing page (one call per page, not one per image)

DO NOT USE WHEN:

• Waiting for assets to finish ingest → POST /api/v1/assets/status (nothing signed)
• You want the full-size bytes → GET /api/v1/assets/{id}/content
• You want a stable public URL → publish the asset and use publicUrl