Add demo.sh — shell wrapper for raw terminal mode

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.

demo.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+# cl-tty demo launcher
+# Sets raw terminal mode before starting SBCL, restores on exit.
+# Raw mode is needed so individual keystrokes are captured instead
+# of being line-buffered and echoed by the terminal driver.
+
+SAVED=$(stty -g 2>/dev/null)
+if [ -z "$SAVED" ]; then
+    echo "ERROR: Not running in a real terminal." >&2
+    exit 1
+fi
+
+cleanup() { stty "$SAVED" 2>/dev/null; }
+trap cleanup EXIT INT TERM
+
+stty raw -echo -isig -icanon min 1 time 0 2>/dev/null
+sbcl --script "$(dirname "$0")/demo.lisp"