Bulk render many items to stored URLs

Render MANY images in one call — the same design in several sizes, the same design with different data, a mix of designs, or the ordered slides of a CAROUSEL. Authenticate with a render key (dma-api-key) as a header or ?dma-api-key= query param. Send { "items": [ ... ] } (1-25); each item is rendered and stored, returning a URL. results preserves input order (result[i] ↔ items[i]), so for a carousel the array IS the slide sequence. Request-level delivery/format/quality/expiresIn are defaults; any item may override format/quality/variation/overrides. Each item is one metered render (N items = N renders); a failed item does not abort the rest.