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

docs/ARCHITECTURE.org

@@ -1,10 +1,10 @@
-#+TITLE: cl-tui Architecture
+#+TITLE: cl-tty Architecture
 #+STARTUP: content
-#+FILETAGS: :project:cl-tui:architecture:
+#+FILETAGS: :project:cl-tty:architecture:
 
 * Architecture
 
-cl-tui is a layered framework. Each layer has a single responsibility
+cl-tty is a layered framework. Each layer has a single responsibility
 and communicates with adjacent layers through a well-defined protocol.
 
 ** Layer Diagram
@@ -264,9 +264,9 @@ reads terminal background color at startup.
 ** File Structure
 
 #+BEGIN_SRC
-  cl-tui/
-  ├── cl-tui.asd
-  ├── cl-tui-tests.asd
+  cl-tty/
+  ├── cl-tty.asd
+  ├── cl-tty-tests.asd
   ├── README.org
   ├── LICENSE
   ├── docs/