Names the widths the site's own images come in. Every image the API serves
(avatars, covers, thumbnails, attachments, proxied images) takes ?w= and
answers a copy scaled down to it, so a card or an avatar doesn't load the
upload at full size. The frontend builds those URLs from this list
(imageSrcSet in src/utils/shared/urls.ts) and the server makes no other
width (serveImage in api/lib/upload.ts), which bounds what it keeps.
Usage
import * as mod from "shared/image.ts";