dsh-quicklook: Quick Look Preview in the Sidebar

`dsh-quicklook` is a companion plugin for DeepSeek Harness that provides QuickLook-style quick previews. Press Space to display images, PDFs, or text content as an overlay in the current context. The plugin supports zoom memory and hot-swapping, but depends on `dsh-better-sidebar`. It requires a specific Node.js version and becomes available after installation and restart, aiming to improve file browsing efficiency.