SXC content: docs/examples/home/reference pages + SX testing runner

New sxc/ content tree with 120 page files across docs, examples, home,
and reference demos. sx/sx/testing/ adds page-runner.sx (317L) and
index-runner.sx (394L) — SX-native test runner pages for
browser-based evaluation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

sx/sxc/examples/edit-row-demo.sx

@@ -0,0 +1,23 @@
+(defcomp
+  (&key rows)
+  (div
+    (table
+      (~tw :tokens "w-full text-left text-sm")
+      (thead
+        (tr
+          (~tw :tokens "border-b border-stone-200")
+          (th (~tw :tokens "px-3 py-2 font-medium text-stone-600") "Name")
+          (th (~tw :tokens "px-3 py-2 font-medium text-stone-600") "Price")
+          (th (~tw :tokens "px-3 py-2 font-medium text-stone-600") "Stock")
+          (th (~tw :tokens "px-3 py-2 font-medium text-stone-600 w-24") "")))
+      (tbody
+        :id "edit-rows"
+        (map
+          (fn
+            (row)
+            (~examples/edit-row-view
+              :id (nth row 0)
+              :name (nth row 1)
+              :price (nth row 2)
+              :stock (nth row 3)))
+          rows)))))