Raw terminal mode must be set by the parent process (the shell),
not from inside SBCL. sb-ext:run-program subprocesses cannot
reliably access the controlling terminal for stty operations.
./demo.sh sets raw mode via stty, runs sbcl --script demo.lisp,
and restores terminal state on exit (EXIT, INT, TERM).
demo.lisp no longer calls with-raw-terminal — it assumes the
calling shell has already set raw mode.
