dsh-client-sidebar-overlay: Sidebar Overlay

This plugin is designed to resolve layout conflicts when DeepSeek Harness is embedded in VS Code's narrow sidebar by converting the sidebar into an on-demand floating layer. Core features include: invoking the floating layer by clicking the whale icon in the session header, supporting left/right side switching, fixing `fixed` positioning, and intercepting pop-up layers to prevent them from flying off-screen. Installation requires copying the files to `node_modules` and adding a mount entry in the configuration. It is compatible with the DSH 0.1.0-rc.7 environment.