Rename cl-tui -> cl-tty, v0.9.0: Dialog System + Toast

Rename: cl-tty avoids naming collision with Quicklisp's cl-tui (naryl/cl-tui,
a cl-charms-based ncurses library). Our project is pure escape-sequence CL.

v0.9.0 adds:
- Dialog base class: modal overlay with backdrop, centered panel, size
  variants (:small/:medium/:large), stack-based management
- Dialog subclasses: alert, confirm, select-dialog, prompt-dialog
- Toast notifications: transient, top-right corner, auto-dismiss,
  colored variants (info/success/warning/error)
- 78 tests total, 100% passing

ASDF: read-time package references (+fiveam:+) replaced with
find-symbol so .asd loads without FiveAM pre-loaded

demo.lisp

@@ -1,4 +1,4 @@
-;; demo.lisp — minimal cl-tui demo
+;; demo.lisp — minimal cl-tty demo
 (load "/root/quicklisp/setup.lisp")
 (ql:quickload :fiveam :silent t)
 (load "backend/package.lisp")
@@ -11,7 +11,7 @@
 (load "src/components/box.lisp")
 (load "src/components/text.lisp")
 (load "src/components/render.lisp")
-(in-package :cl-tui.box)
+(in-package :cl-tty.box)
 
 ;; Demo 1: Simple backend (ASCII)
 (let* ((b (make-simple-backend))
@@ -21,7 +21,7 @@
 
 ;; Demo 2: Box with text inside
 (let* ((b (make-simple-backend))
-       (tx (make-text "This is cl-tui in action!" :width 28 :height 1)))
+       (tx (make-text "This is cl-tty in action!" :width 28 :height 1)))
   (setf (layout-node-direction (text-layout-node tx)) :column)
   (compute-layout (text-layout-node tx) 28 1)
   (render tx b)