dsh-plugin-git-bash: Enabling DSH to Use Git Bash by Default on Windows

`dsh-plugin-git-bash` is a plugin for DSH designed to replace PowerShell with Git for Windows Bash as the default shell in Windows environments, while fully preserving DSH's original permission semantics of `read-only`, `workspace-write`, and `danger-full-access`. This plugin is installed as a bundle layer into the DSH profile without modifying the main DSH installation directory, and supports the `standard`, `code`, `cordis`, and `minimal` presets as well as the Web Agent for uniformly executing commands via Git Bash.