dsh-screenshot-paste: File Clipboard Functionality for DeepSeek Harness Web GUI

`dsh-screenshot-paste` is a purely external plugin for DeepSeek Harness, designed to solve the cumbersome issue of passing local files to agents. It supports adding files via Ctrl+V, drag-and-drop, or click-to-upload (supporting images, PDFs, and various other formats), and displays them as reference chips. When a message is sent, the plugin automatically appends the file paths. It features automatic directory migration, security restrictions, and zero input-box pollution, enabling convenient local file handling through the GUI after installation.