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/backend-protocol.org

@@ -1,6 +1,6 @@
-#+TITLE: cl-tui Backend Protocol — v0.0.1
+#+TITLE: cl-tty Backend Protocol — v0.0.1
 #+STARTUP: content
-#+FILETAGS: :cl-tui:backend:v0.0.1:
+#+FILETAGS: :cl-tty:backend:v0.0.1:
 #+OPTIONS: ^:nil
 
 * Backend Protocol
@@ -119,10 +119,10 @@ Borders:
 ** Test Suite
 
 #+BEGIN_SRC lisp
-(defpackage :cl-tui-backend-test
+(defpackage :cl-tty-backend-test
   (:use :cl :fiveam)
   (:export #:run!))
-(in-package :cl-tui-backend-test)
+(in-package :cl-tty-backend-test)
 
 (def-suite backend-suite :description "Backend protocol tests")
 (in-suite backend-suite)
@@ -224,7 +224,7 @@ Borders:
 *** Package
 
 #+BEGIN_SRC lisp
-(defpackage :cl-tui.backend
+(defpackage :cl-tty.backend
   (:use :cl)
   (:export
    ;; Backend classes
@@ -245,7 +245,7 @@ Borders:
    #:capable-p
    ;; Constructors
    #:make-simple-backend))
-(in-package :cl-tui.backend)
+(in-package :cl-tty.backend)
 #+END_SRC
 
 *** Backend Base Class