dsh-focus-overlay: Focus mode for DSH Web GUI

`dsh-focus-overlay` is an MIT-licensed community plugin developed by boogoo619, specifically designed to provide a full-screen focus reading mode for the DSH Web GUI. By hiding the title bar, input area, and sidebar, and collapsing the AI tool invocation flow into a summary, it reduces interface clutter, allowing users to focus on reading the conversation and supporting in-place replies. Core features include right-side node navigation, quick activation via the 'F' key, new reply notifications, linkification of file mentions, and Chinese/English support, with compatibility for DSH-better-sidebar. Installation requires a dsh CLI >= 0.1.0-rc.5 and Node.js >= 22.19.0 environment, and can be installed via the `dsh plugin` command from npm or GitHub; `dsh w` must be restarted after installation.