* fix: make subprocess and symlink tests Windows-compatible
- Gate preexec_fn (POSIX-only) so optional tools can run on Windows
- Skip symlink tests when the platform denies the privilege
- Add a Windows CI leg and a Windows CLI smoke run
* fix: use UTF-8 stdio and fail Windows smoke on first error
- Reconfigure stdin/stdout/stderr to UTF-8 so Windows redirected streams
stop raising UnicodeEncodeError on invisible Unicode characters
- Chain the Windows smoke commands so a failing script fails the step