Introducing DSH Plugins: Agent Shell and the Shell Drawer

`dsh-agent-shell` is a client plugin for DeepSeek Harness that provides command execution and visual feedback. It registers the `bash`, `cmd`, and `shell_drawer` tools and uses a loopback RPC channel to push execution results in real time to the Shell drawer on the right, supporting timeouts, output truncation, and manual control. Installation requires a dependency on `dsh-right-drawer`. It enables system commands to be executed through conversation or tool instructions, making it suitable for automated testing and debugging scenarios.