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/scroll-items.sx

@@ -0,0 +1,20 @@
+(defcomp
+  (&key items page)
+  (<>
+    (map
+      (fn
+        (item)
+        (div
+          (~tw :tokens "px-4 py-3 border-b border-stone-100 text-sm text-stone-700")
+          item))
+      items)
+    (when
+      (<= page 5)
+      (div
+        :id "scroll-sentinel"
+        :sx-get (str "/sx/(geography.(hypermedia.(example.(api.scroll))))?page=" page)
+        :sx-trigger "intersect once"
+        :sx-target "#scroll-items"
+        :sx-swap "beforeend"
+        (~tw :tokens "p-3 text-center text-stone-400 text-sm")
+        "Loading more..."))))