dsh-advanced-sidebar: Sidebar Extension for DeepSeek Harness Web Client

The default feature set of the DeepSeek Harness Web Client is limited, and the `navid-kianfar/dsh-advanced-sidebar` plugin adds capabilities for Git, terminal use, file browsing, and background tasks through a side dock. The plugin uses host processes to run operations that cannot be executed in the browser, supports session management, file preview, and four preview modes (Server, File, URL, and Scratchpad), and provides Git staging, committing, pushing, and interactive terminal management.