remove: old scrollbox-tabbar.org (all prose distributed to per-module orgs)

The combined org file had no unique content — all prose and code were
already in scrollbox.org, tabbar.org, and container-package.org. The
old file's code blocks had the pre-bugfix render/draw-scrollbars
versions and all had :tangle no.

Also update README.org and ARCHITECTURE.org references from
scrollbox-tabbar.org to the individual org files.

README.org

@@ -207,7 +207,7 @@ line joining on backspace. See ~org/text-input.org~.
 
 Scrollable viewport with a list of children. Only renders children
 intersecting the visible area (viewport culling). Scrollbars drawn
-at the right/bottom edges. See ~org/scrollbox-tabbar.org~.
+at the right/bottom edges. See ~org/scrollbox.org~.
 
 #+BEGIN_SRC lisp
 (make-scroll-box &key children scroll-y scroll-x sticky-scroll-p)
@@ -217,7 +217,7 @@ at the right/bottom edges. See ~org/scrollbox-tabbar.org~.
 *** TabBar
 
 Horizontal tab navigation. Renders tab labels, highlights active tab.
-Left/right arrows cycle through tabs. See ~org/scrollbox-tabbar.org~.
+Left/right arrows cycle through tabs. See ~org/tabbar.org~.
 
 #+BEGIN_SRC lisp
 (make-tab-bar &key tabs active)
@@ -356,7 +356,9 @@ cl-tty/
 ├── tests/                  # Test files
 ├── org/                    # Literate source files
 │   ├── text-input.org
-│   ├── scrollbox-tabbar.org
+│   ├── scrollbox.org
+│   ├── tabbar.org
+│   ├── container-package.org
 │   ├── dialog.org
 │   ├── mouse.org
 │   ├── select.org