Mutation - prepareFileLibraryUploads

Prepares File Library metadata and signed direct-upload URLs for one to 20 files. Each path must include a root segment and use forward slashes with 2–10 segments, be at most 2048 characters, and imply at most 40 unique folders. The client must PUT binary bytes outside GraphQL using Content-Type from the result and x-amz-acl: private when required by the signed URL. URLs expire after 15 minutes while pending. Reuse the same uploadKey and manifest to retry without creating duplicates; split larger batches into chunks with the same key. Access: Authenticated users with write access to the workspace and parent folder. Errors: Throws for invalid paths, inaccessible parents, or conflicting retries.