Send files, images, and audio messages via Feishu Lark API using the mandatory two-step process. Use when needing to send files, images, or voice messages to Feishu users or groups. This skill enforces the required workflow - first upload to get file_key, image_key, or audio_key, then send message with the key. Supports file API for documents, image API for pictures, and file API with audio type for voice messages.