File upload and blob storage for a Next.js 16 site — dropzone UX with drag-drop as enhancement over a real file input, true progress from XHR upload events, instant client validation of type and size, zod v4 re-validation on the server, Vercel Blob as the default store with S3-compatible (S3/R2) as the alternative, server-generated storage keys, and post-upload rendering through next/image with persisted dimensions.
