fdtree: A Workspace File Tree and Real-Time Diff Plugin for DeepSeek Harness

`fdtree` is a plugin-based file browsing and diff tool for DeepSeek Harness (DSH). It uses a four-column layout to embed the file directory tree and real-time diff views in the interface, supporting multi-tab viewing of code changes. The plugin offers smart mode switching (Git and baseline), multilingual syntax highlighting, and terminal integration. Its security design includes zero external requests, local Git execution, and session isolation, ensuring that it only reads local files and does not connect to the network.