Design a file upload feature for an AI chat application.

Focus on the user experience and technical feasibility of the file upload feature within the context of an AI chat application. Consider the types of files users might want to upload (e.g., images, documents, audio) and how these files will enhance the chat experience. Discuss the user interface design, including drag-and-drop functionality and progress indicators. Address backend considerations such as file storage, security (e.g., virus scanning), and handling file size limits. Finally, think about how the AI can interact with the uploaded files, such as analyzing content or providing contextual responses based on the uploaded material.