/terminal-setup contradicts itself on Windows Terminal

Bug description

/terminal-setup displays a self-contradictory message on Windows: it says the command cannot be run from windows-terminal, then in the same output instructs the user to run it in Windows Terminal.

Steps to reproduce

1. Open Claude Code in Windows Terminal
2. Run /terminal-setup

Actual output

Terminal setup cannot be run from windows-terminal.

This command configures a convenient Shift+Enter shortcut for multi-line prompts.
Note: You can already use backslash (\) + return to add newlines.

To set up the shortcut (optional):
1. Exit tmux/screen temporarily
2. Run /terminal-setup directly in one of these terminals:
   • Windows: Windows Terminal
   • IDE: VSCode, Cursor, Windsurf, Zed
   • Other: Alacritty
3. Return to tmux/screen - settings will persist

Expected behavior

Either:

• The command should work in Windows Terminal (fix the detection logic), or
• The instructions should not list Windows Terminal as a supported terminal if it is explicitly blocked

Additional context

• The error message also mentions "exit tmux/screen temporarily", but the user never started tmux or screen — Claude Code appears to be falsely detecting the Windows Terminal environment as a multiplexer session.
• Platform: Windows 11 Enterprise (win32)
• Shell: bash