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

src/components/markdown.lisp

@@ -1,6 +1,6 @@
-;;; markdown.lisp — Markdown + Code + Diff rendering for cl-tui
+;;; markdown.lisp — Markdown + Code + Diff rendering for cl-tty
 
-(in-package :cl-tui.markdown)
+(in-package :cl-tty.markdown)
 
 ;; ─── Node constructors ────────────────────────────────────────────────────────