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/reference/ref-sync-demo.sx

@@ -0,0 +1,21 @@
+(defcomp
+  ()
+  (div
+    (~tw :tokens "space-y-3")
+    (input
+      :type "text"
+      :name "q"
+      :placeholder "Type quickly..."
+      :sx-get "/sx/(geography.(hypermedia.(reference.(api.slow-echo))))"
+      :sx-trigger "input changed delay:100ms"
+      :sx-sync "replace"
+      :sx-target "#ref-sync-result"
+      :sx-swap "innerHTML"
+      (~tw :tokens "w-full px-3 py-2 border border-stone-300 rounded text-sm focus:outline-none focus:ring-2 focus:ring-violet-500"))
+    (p
+      (~tw :tokens "text-xs text-stone-400")
+      "With sync:replace, each new keystroke aborts the in-flight request.")
+    (div
+      :id "ref-sync-result"
+      (~tw :tokens "p-3 rounded bg-stone-100 text-stone-400 text-sm")
+      "Type to see only the latest result.")))