dsh-gitbash-shell: Git Bash Executor Plugin for Windows

This plugin is designed to replace the default PowerShell Shell with Git Bash on Windows for DeepSeek Harness (DSH). Key features include disabling `pwsh-sandbox` and enabling a Git Bash executor; automatically generating four Git Bash presets (Standard, Minimal, PTC, and Creative); supporting POSIX path conversion; and ensuring compatibility with multiple DSH versions. After installation, the host must be restarted. The Bash path, timeout, and preset mode can be customized through a configuration file. The plugin resolves path-handling issues in Git workflows on Windows, improving DSH's compatibility and user experience on the platform.