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.lisp

@@ -1,9 +1,5 @@
 ;;; demo.lisp — cl-tty interactive demo
 ;;; Run: sbcl --script demo.lisp
-;;;
-;;; Demonstrates: backend detection, raw terminal mode, key/mouse input,
-;;; layout engine, component rendering pipeline, framebuffer diff flush,
-;;; text-input, textarea, select, dialog, scrollbox, tabbar.
 
 ;; Load cl-tty directly via ASDF (no Quicklisp dependency needed —
 ;; sb-posix is built into SBCL, no external libraries required).
@@ -124,10 +120,8 @@
      t)))
 
 (defun run-demo ()
-  "Run the demo.  Assumes raw terminal mode is already set by the
-shell wrapper (./demo) or by running:
-  stty raw -echo -isig -icanon min 1 time 0
-  sbcl --script demo.lisp"
+  "Run the demo.  Raw terminal mode should already be set by the
+./demo.sh shell wrapper."
   (init-app-state)
   (let* ((backend (detect-backend))
          (w 80) (h 24))