v1.0.0 review fixes: dialog, textarea, scrollbox, demo, ASDF, layout

Fixes from subagent code review (15 findings):

CRITICAL runtime bugs:
- dialog.lisp: backend-write calls -> draw-rect/draw-text (wrong arg count)
- dialog.lisp: removed undefined render-component call
- dialog.lisp: toast render backend-write -> draw-text

MAJOR data loss / silent failures:
- textarea.lisp: undo overflow now drops oldest entry instead of wiping stack
- scrollbox.lisp: :background-element -> :bright-black (theme keyword never resolved)

ASDF completeness:
- modern-tests.lisp wired as component and test-op suite
- layout tests added to test-op suite list
- markdown suite lookup now uses keyword (was looking up wrong string)
- test runner updated to match

API cleanup:
- container-package: removed duplicate render export
- select-package: removed duplicate render export
- markdown.lisp: #\Escape -> #\Esc for consistency
- textarea.lisp: removed duplicate %split-string defn

Demo robustness:
- Added unwind-protect for guaranteed terminal cleanup
- Uses make-modern-backend constructor
- Uses set-raw-mode/restore-terminal-state

Layout:
- normalize-box handles partial padding specs (was returning all zeros)

src/components/textarea.lisp

@@ -1,16 +1,5 @@
 (in-package #:cl-tty.input)
 
-;;; ---------------------------------------------------------------------------
-;;; Utility: split string (local copy for dependency-free operation)
-;;; ---------------------------------------------------------------------------
-(defun %split-string (string separator)
-  "Split STRING at each occurrence of SEPARATOR. Returns list of strings."
-  (loop with start = 0
-        for pos = (position separator string :start start)
-        collect (subseq string start pos)
-        while pos
-        do (setf start (1+ pos))))
-
 ;;; ---------------------------------------------------------------------------
 ;;; Textarea class
 ;;; ---------------------------------------------------------------------------
@@ -169,10 +158,10 @@
   "Save current value on undo stack."
   (let ((stack (textarea-undo-stack ta)))
     (when (>= (length stack) (array-total-size stack))
-      (setf (textarea-undo-stack ta)
-            (make-array 100 :fill-pointer 0)))
+      (loop for i from 1 below (length stack)
+            do (setf (aref stack (1- i)) (aref stack i)))
+      (decf (fill-pointer stack)))
     (vector-push (textarea-value ta) stack)
-    ;; Clear redo stack on new action
     (setf (fill-pointer (textarea-redo-stack ta)) 0)))
 
 (defun textarea-undo (ta)