Add UtilS3Upload node that uploads images/text to S3-compatible storage (AWS S3, Cloudflare R2, MinIO) via presigned URL HTTP PUT. No external dependencies required — uses Python stdlib urllib only. - Remove obsolete LayerSeparation PRD and paper draft docs - Add S3 Upload PRD document Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>