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/lazy-loading-demo.sx

@@ -0,0 +1,17 @@
+(defcomp
+  ()
+  (div
+    (~tw :tokens "space-y-4")
+    (p
+      (~tw :tokens "text-sm text-stone-500")
+      "The content below loads automatically when the page renders.")
+    (div
+      :id "lazy-target"
+      :sx-get "/sx/(geography.(hypermedia.(example.(api.lazy))))"
+      :sx-trigger "load"
+      :sx-swap "innerHTML"
+      (~tw :tokens "p-6 rounded border border-stone-200 bg-stone-100 text-center")
+      (div
+        (~tw :tokens "animate-pulse space-y-2")
+        (div (~tw :tokens "h-4 bg-stone-200 rounded w-3/4 mx-auto"))
+        (div (~tw :tokens "h-4 bg-stone-200 rounded w-1/2 mx-auto"))))))