Import assets from public URLs

Fetches 1-10 public http(s) URLs server-side, one at a time, and stores each as a ready asset with no upload or finalize step. Media only: images, fonts, PDF, audio, video, dotLottie, and Rive; text, data, documents, and archives are refused. Images, fonts, and PDFs must parse as what they claim, hosts on private addresses are rejected, the upload kind and MIME rules apply, and each download is capped at 30 MiB (larger files must be uploaded directly). Each item may carry a description and, for images, a category. Name each item by url, or by photo: the number over a picture on contact sheets webResearch.profile or webResearch.viewImage showed you, which saves copying its long signed link. assets carries successes with CDN URLs and sourceUrl; errors carries failures typed invalid_url, non_public_address, unreachable, too_large, unsupported_type, signature_expired, or unknown_photo (a number you were not shown or that expired; look at the pictures again for current numbers). Import only assets you have the right to use.