Windows Terminal incorrectly detected as tmux/screen in /terminal-setup

Bug Description

When running /terminal-setup in Windows Terminal (without tmux/screen), Claude Code incorrectly detects the terminal as running inside tmux/screen and displays:

Terminal setup cannot be run from windows-terminal.

Environment

• OS: Windows
• Terminal: Windows Terminal (native, no tmux/screen)
• Claude Code: Latest version

Steps to Reproduce

1. Open Windows Terminal (not inside tmux/screen)
2. Run Claude Code
3. Execute /terminal-setup

Expected Behavior

Should recognize Windows Terminal and allow Shift+Enter shortcut configuration.

Actual Behavior

Shows error message claiming it cannot run from "windows-terminal" and suggests exiting tmux/screen, even though tmux/screen is not being used.

The message is also confusing because it says:

• "Terminal setup cannot be run from windows-terminal"
• But then lists "Windows: Windows Terminal" as a supported terminal

Impact

Low - workaround exists (using \ + Enter for newlines), but the detection logic appears to have a bug.