literate: convert org/layout-engine.org from doc-only to tangle source

Now tangles to layout.lisp + layout/tests.lisp.
Deleted hand-written originals and regenerated — GREEN.

src/layout/tests.lisp

@@ -122,14 +122,12 @@
 ;; ── Edge Cases ────────────────────────────────────────────────
 
 (test empty-container-does-not-crash
-  "compute-layout on a node with no children should not error"
   (let ((r (make-layout-node)))
     (compute-layout r 20 20)
     (is (integerp (layout-node-width r)))
     (is (integerp (layout-node-height r)))))
 
 (test single-child-in-column
-  "A column with one child places it correctly"
   (let* ((r (make-layout-node :direction :column :width 10 :height 20))
          (c (make-layout-node :height 5)))
     (layout-node-add-child r c)
@@ -138,7 +136,6 @@
     (is (= (layout-node-height c) 5))))
 
 (test zero-size-container
-  "compute-layout with zero available space should not error"
   (let* ((r (make-layout-node :direction :column))
          (c (make-layout-node :height 5)))
     (layout-node-add-child r c)
@@ -147,17 +144,15 @@
     (is (integerp (layout-node-y c)))))
 
 (test deep-nesting-three-levels
-  "Three-level deep nesting produces correct leaf positions"
-  (let* ((out (vbox ()                                    ; outer box
-                (vbox (:grow 1)                           ; middle box
-                  (make-layout-node :height 2))))         ; leaf
+  (let* ((out (vbox ()
+                (vbox (:grow 1)
+                  (make-layout-node :height 2))))
          (leaf (elt (layout-node-children
                       (elt (layout-node-children out) 0)) 0)))
     (compute-layout out 20 20)
     (is (= (layout-node-y leaf) 0))))
 
 (test large-padding-leaves-room
-  "Large padding reduces content area but doesn't crash"
   (let* ((r (make-layout-node :direction :column
                               :padding '(:top 5 :left 5 :bottom 5 :right 5)))
          (c (make-layout-node :height 3)))
@@ -167,7 +162,6 @@
     (is (= (layout-node-y c) 5))))
 
 (test negative-grow-is-clamped
-  "Grow values are adjusted but still compute"
   (let* ((r (make-layout-node :direction :row :width 10))
          (c (make-layout-node :width 5 :grow -1)))
     (layout-node-add-child r c)