dsh-edit-guardian: File Change Visualization and Command Safety Gate

`dsh-edit-guardian` is a DeepSeek Harness Web plugin designed to address the lack of visibility and blocking capabilities when an Agent modifies files or executes Shell commands. Core features include: 1. **File Change Visualization**: Displays modified line counts and inline diffs in real time, with changes summarized in the persistence bar. 2. **Retain and Undo**: Supports retaining or reverting changes for a single file or batch operations, using the backend `/undo` command to restore file states. 3. **Safety Approval**: Intercepts destructive commands such as `rm` and `git reset` in `bash`, `pwsh`, and other shells, and prevents accidental operations through highlighting and a popup approval workflow. The plugin takes effect after installation and a Web process restart.