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

layout/layout.lisp

@@ -1,6 +1,6 @@
 ;;; layout — Pure CL Flexbox layout engine
 
-(defpackage :cl-tui.layout
+(defpackage :cl-tty.layout
   (:use :cl)
   (:export
    #:layout-node #:make-layout-node
@@ -16,7 +16,7 @@
    #:layout-node-fixed-height #:normalize-box
    #:box-edge))
 
-(in-package :cl-tui.layout)
+(in-package :cl-tty.layout)
 
 (defun normalize-box (spec)
   (cond ((null spec) '(:top 0 :right 0 :bottom 0 :left 0))

layout/tests.lisp

@@ -1,7 +1,7 @@
-(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)