[Feature Request] Add environment variable to identify CLI shell type (Bash/PowerShell/CMD)

Question

**Bug Description**
Provide a way of configuring an environment variable we can use to signal to Claude what CLI tool we're using to access it (Bash vs PowerShell vs CMD)

**Environment Info**
- Platform: win32
- Terminal: windows-terminal
- Version: 2.0.76
- Feedback ID: ba572eab-5a5d-491b-b2cb-67ca0ac6352c

**Errors**
```json
[]
```