DeepSeek Harness Plugin: dsh-workspace-overlay

`dsh-workspace-overlay` is an out-of-tree DSH plugin designed to address multi-workspace configuration isolation and dynamic updates. It enables managing multi-environment configurations without restarting the host by providing a shared `workspaceCordis` scope, supporting Composition hot reloading, Agent integration, and a Workspace-aware MCP manager. It supports hot reloading (watching `.dsh/cordis.yml` by default) but has limitations, such as not watching certain files and not supporting Provider HMR.