Upload a file for use in social content and create the corresponding content entry. The file format is automatically detected from the uploaded file's content type. Supported formats include images (JPG, PNG, GIF, WEBP, BMP, TIFF), videos (MP4, MOV, AVI), and documents (PDF, PPT, PPTX, DOC, DOCX). Maximum file size is 650 MB. The full response object returned by this operation is used to attach the file to social content — pass the entire object (contentId, fileName, contentFormat) as an entry in the attachments array when creating or updating a social content item. For example, an assistant can call this operation while coordinating channel-service workflows to retrieve or change authoritative records before executing dependent user-facing actions.