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/container-package.lisp

@@ -9,5 +9,4 @@
    #:tab-bar #:make-tab-bar
    #:tab-bar-active #:tab-bar-tabs
    #:tab-bar-add #:tab-bar-next #:tab-bar-prev
-   #:tab-bar-select #:tab-bar-handle-key
-   #:render))
+   #:tab-bar-select #:tab-bar-handle-key))