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

org/layout-engine.org

@@ -1,6 +1,6 @@
-#+TITLE: cl-tui Layout Engine — v0.0.3
+#+TITLE: cl-tty Layout Engine — v0.0.3
 #+STARTUP: content
-#+FILETAGS: :cl-tui:layout:v0.0.3:
+#+FILETAGS: :cl-tty:layout:v0.0.3:
 #+OPTIONS: ^:nil
 
 * Layout Engine
@@ -85,10 +85,10 @@ means a full Yoga FFI binding is unnecessary — ~200 lines of CL math.
 ** Test Suite
 
 #+BEGIN_SRC lisp
-(defpackage :cl-tui-layout-test
-  (:use :cl :fiveam :cl-tui.layout)
+(defpackage :cl-tty-layout-test
+  (:use :cl :fiveam :cl-tty.layout)
   (:export #:run-tests))
-(in-package :cl-tui-layout-test)
+(in-package :cl-tty-layout-test)
 
 (def-suite layout-suite :description "Layout engine tests")
 (in-suite layout-suite)
@@ -288,7 +288,7 @@ means a full Yoga FFI binding is unnecessary — ~200 lines of CL math.
 *** Package
 
 #+BEGIN_SRC lisp
-(defpackage :cl-tui.layout
+(defpackage :cl-tty.layout
   (:use :cl)
   (:export
    ;; Classes
@@ -306,7 +306,7 @@ means a full Yoga FFI binding is unnecessary — ~200 lines of CL math.
    #:compute-layout
    ;; Macros
    #:vbox #:hbox #:spacer))
-(in-package :cl-tui.layout)
+(in-package :cl-tty.layout)
 #+END_SRC
 
 *** Layout Node Class