dsh-git-flow: DeepSeek Harness Workspace Git Plugin

`dsh-git-flow` is a plugin in DeepSeek Harness for managing repositories within a session context. It provides branch browsing, switching, creation, and committing, with AI-generated commit messages. Installation requires Node.js ^22.19.0 or 24.0.0 and pnpm 10. Its security design implements session isolation, secure command execution, prohibition of force pushes, restricted commit scope, and forced branch switching only after confirmation, ensuring safe and controllable operations.