dsh-composer-image-tools: Add image and area screenshot entry to the DSH chat input

`dsh-composer-image-tools` is an MIT-licensed DSH plugin maintained by ai-yucheng, featuring zero dependencies and a custom implementation. Designed to address the lack of a unified image entry point in chat input boxes, this plugin adds toolbar buttons to support local image uploads and custom area screenshots, injecting images into the DSH draft track to be sent with messages. Core features include support for multi-select image uploads, with automatic interception of files exceeding 10MB to save tokens. It provides a full-screen mask-style area screenshot feature based on Electron's main process `desktopCapturer`, supporting mouse drag selection, automatic cropping, and cancellation via `Esc`, without relying on WeChat or external tools. Additionally, it is compatible with clipboard pasting (`Ctrl+V`) and integrates with the plugin's built-in screenshot functionality.