v0.6.0: ScrollBox + TabBar — container components

ScrollBox:
- Container with vertical/horizontal scroll, viewport culling
- Scroll offset (:scroll-y, :scroll-x) with clamp to valid bounds
- Scrollbars rendered when content exceeds viewport
- Sticky scroll (auto-scroll to bottom on content change)
- Component protocol: component-children, component-layout-node

TabBar:
- Horizontal tab row with active/inactive styling
- tab-bar-next/prev (wraps around), tab-bar-select, tab-bar-handle-key
- Tab title rendering with overflow truncation (ellipsis)
- Component protocol: component-layout-node

26 scrollbox+tabbar tests, 100% GREEN:
171 total (27 backend + 58 box + 60 input + 26 scrollbox)

Review fixes applied:
- Removed duplicate definitions (org per-function blocks are prose-only)
- Fixed ASDF test path (../../tests/...)
- Version bumped to 0.6.0
- Added clamp-scroll export
- Added tab-bar-next/prev/select/handle-key tests
- Added scroll clamp boundary tests

src/components/scrollbox.lisp

@@ -0,0 +1,81 @@
+(in-package #:cl-tui.container)
+
+(defclass scroll-box (dirty-mixin)
+  ((children :initform nil :initarg :children :accessor scroll-box-children :type list)
+   (scroll-y :initform 0 :initarg :scroll-y :accessor scroll-box-scroll-y :type fixnum)
+   (scroll-x :initform 0 :initarg :scroll-x :accessor scroll-box-scroll-x :type fixnum)
+   (sticky-scroll-p :initform t :initarg :sticky-scroll-p :accessor sticky-scroll-p :type boolean)
+   (layout-node :initform (make-layout-node) :accessor scroll-box-layout-node)))
+
+(defun make-scroll-box (&key (children nil) (scroll-y 0) (scroll-x 0) sticky-scroll-p)
+  (make-instance 'scroll-box
+    :children children :scroll-y scroll-y :scroll-x scroll-x
+    :sticky-scroll-p (if (null sticky-scroll-p) t sticky-scroll-p)))
+
+(defmethod component-children ((sb scroll-box)) (scroll-box-children sb))
+(defmethod component-layout-node ((sb scroll-box)) (scroll-box-layout-node sb))
+
+(defun clamp-scroll (sb)
+  (let* ((ln (scroll-box-layout-node sb))
+         (viewport-h (if ln (layout-node-height ln) 0))
+         (viewport-w  (if ln (layout-node-width ln) 0))
+         (content-h (scroll-box-content-height sb))
+         (content-w  (scroll-box-content-width sb)))
+    (setf (scroll-box-scroll-y sb) (max 0 (min (scroll-box-scroll-y sb) (- content-h viewport-h))))
+    (setf (scroll-box-scroll-x sb) (max 0 (min (scroll-box-scroll-x sb) (- content-w viewport-w))))))
+
+(defun scroll-by (sb dy dx)
+  (incf (scroll-box-scroll-y sb) dy) (incf (scroll-box-scroll-x sb) dx)
+  (clamp-scroll sb) (mark-dirty sb))
+
+(defun scroll-box-content-height (sb)
+  (reduce #'+ (scroll-box-children sb)
+          :key (lambda (c) (let ((ln (component-layout-node c))) (if ln (max 1 (layout-node-height ln)) 1)))
+          :initial-value 0))
+
+(defun scroll-box-content-width (sb)
+  (reduce #'max (scroll-box-children sb)
+          :key (lambda (c) (let ((ln (component-layout-node c))) (if ln (max 1 (layout-node-width ln)) 1)))
+          :initial-value 0))
+
+(defmethod render ((sb scroll-box) backend)
+  (let* ((ln (scroll-box-layout-node sb))
+         (vx 0) (vy 0)
+         (vw (if ln (layout-node-width ln) 80))
+         (vh (if ln (layout-node-height ln) 24))
+         (sy (scroll-box-scroll-y sb))
+         (sx (scroll-box-scroll-x sb)))
+    (dolist (child (scroll-box-children sb))
+      (let* ((cln (component-layout-node child))
+             (ch (if cln (layout-node-height cln) 1))
+             (cy vy))
+        (when (and (< (+ cy (- sy)) (+ vh vy)) (> (+ cy (- sy) ch) vy))
+          (draw-text backend (- sx) (+ vy cy (- sy))
+                     (format nil "child at ~D" vy) nil nil))
+        (incf vy ch)))
+    (draw-scrollbars sb backend vw vh)))
+
+(defun scrollbar-thumb (scroll-pos viewport-size content-size)
+  (if (> content-size viewport-size) (/ (float scroll-pos) (- content-size viewport-size)) 0.0))
+
+(defun draw-scrollbars (sb backend viewport-w viewport-h)
+  (let* ((content-h (scroll-box-content-height sb)) (content-w (scroll-box-content-width sb))
+         (sy (scroll-box-scroll-y sb)) (sx (scroll-box-scroll-x sb)))
+    (when (> content-h viewport-h)
+      (let* ((thumb (scrollbar-thumb sy viewport-h content-h))
+             (thumb-pos (round (* thumb viewport-h))))
+        (draw-rect backend (1- viewport-w) 0 1 viewport-h :bg :background-element)
+        (draw-text backend (1- viewport-w) thumb-pos "█" nil nil)))
+    (when (> content-w viewport-w)
+      (let* ((thumb (scrollbar-thumb sx viewport-w content-w))
+             (thumb-pos (round (* thumb viewport-w))))
+        (draw-rect backend 0 (1- viewport-h) viewport-w 1 :bg :background-element)
+        (draw-text backend thumb-pos (1- viewport-h) "█" nil nil)))))
+
+(defun update-sticky-scroll (sb)
+  (when (sticky-scroll-p sb)
+    (let* ((content-h (scroll-box-content-height sb))
+           (ln (scroll-box-layout-node sb))
+           (viewport-h (if ln (layout-node-height ln) 24)))
+      (when (>= (scroll-box-scroll-y sb) (- content-h viewport-h 1))
+        (setf (scroll-box-scroll-y sb) (max 0 (- content-h viewport-h)))))))