dsh-upload-button: Adding Local Image Upload to the DeepSeek Harness Web GUI

This plugin adds a local image upload button to the left side of the input bar in the DeepSeek Harness Web UI, with multi-select support. It reuses the official drag-and-drop pipeline by synthesizing a DataTransfer object, ensuring consistent image processing logic with zero intrusion. The plugin also includes helper utilities for calling the Tongyi Qianwen API. Users can use it simply by installing the plugin and restarting Harness.