PowerShell tool disabled under MINGW64/Git Bash on Windows

Describe the bug

When Claude Code runs inside Git Bash (MSYS2/MINGW64) on Windows, the PowerShell tool reports "PowerShell is not available on this system" and is disabled — even though:

• platform is correctly detected as win32
• powershell.exe is in PATH at C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe
• PowerShell runs perfectly fine when invoked from Bash: powershell.exe -Command "Write-Host 'works'"

Steps to reproduce

1. Launch Claude Code from a Git Bash (MINGW64) terminal on Windows
2. Try to use the PowerShell tool
3. Observe it says "PowerShell is not available on this system"

Expected behavior

The PowerShell tool should be available on any win32 platform regardless of which shell Claude Code itself is running in. Git Bash is a common setup for Windows developers.

Suggested fix

Instead of disabling the PowerShell tool based on the current shell type, check:

1. Is platform === 'win32'?
2. Is powershell.exe or pwsh.exe in PATH?

If both are true, enable the PowerShell tool. That way it works under Git Bash, MSYS2, MINGW, and any other shell that happens to be the entry point on a Windows system.

Environment

• OS: Windows 11 Home China 10.0.26200
• Shell: MINGW64 Bash (GNU bash 5.2.37)
• Claude Code: current