dsh-doudizhu: Run Doudizhu in a Harness Floating Window

The `dsh-doudizhu` plugin introduces an integrated three-player Dou Dizhu (Fight the Landlord) game to DeepSeek Harness, aiming to address the long waiting cycles agents encounter when processing complex tasks. Through a draggable floating window, it provides a game environment that runs in parallel with the agent, supporting offline single-player mode or AI opponents powered by DeepSeek models. It includes a complete rule engine, a 300-token economy system, quick chat, and task reminders, while ensuring state persistence. The installation command is `dsh plugin --profile web add github:tongji-1/dsh-doudizhu`, and it is primarily intended to provide entertainment and status visibility while waiting for inference results.