dsh-plugin-appshot: DeepSeek Harness Global Window Screenshot Plugin

`dsh-plugin-appshot` is a screenshot plugin for DeepSeek Harness (DSH), designed to streamline the cumbersome manual screenshot workflow. It supports macOS and Windows, allowing users to capture the current window precisely with a global hotkey and automatically inject it into DSH Composer. On macOS, it uses system APIs to automatically bring the window to the foreground, while on Windows, it silently attaches the image. Installation requires granting screen recording and accessibility permissions, and it depends on specific versions of tool libraries. Currently, it supports only specific platforms and native window screenshot functionality.