Replace DeepSeek Harness workspace sidebar with dsh-plugin-ya-workspace-sidebar

`dsh-plugin-ya-workspace-sidebar` is a DSH web interface enhancement plugin maintained by HuanLinOTO, used to replace the official workspace sidebar: the top 5 global recent conversations, the lower-level Workspace→Session secondary menu and breadcrumbs, and conversations are grouped by local date. Operations including search, add, rename, delete, Fork and archive still go through the native Host. The directory installation command is `dsh plugin add github:HuanLinOTO/dsh-plugin-ya-workspace-sidebar`. The current npm version is 0.3.0, licensed under AGPL-3.0. The plugin runs with the permissions of the current dsh process, and the source code should be checked before installation.