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-params-demo.sx

@@ -0,0 +1,28 @@
+(defcomp
+  ()
+  (div
+    (~tw :tokens "space-y-3")
+    (form
+      :sx-post "/sx/(geography.(hypermedia.(reference.(api.echo-vals))))"
+      :sx-target "#ref-params-result"
+      :sx-swap "innerHTML"
+      :sx-params "name"
+      (~tw :tokens "flex gap-2")
+      (input
+        :type "text"
+        :name "name"
+        :placeholder "Name (sent)"
+        (~tw :tokens "flex-1 px-3 py-2 border border-stone-300 rounded text-sm focus:outline-none focus:ring-2 focus:ring-violet-500"))
+      (input
+        :type "text"
+        :name "secret"
+        :placeholder "Secret (filtered)"
+        (~tw :tokens "flex-1 px-3 py-2 border border-stone-300 rounded text-sm focus:outline-none focus:ring-2 focus:ring-violet-500"))
+      (button
+        :type "submit"
+        (~tw :tokens "px-4 py-2 bg-violet-600 text-white rounded hover:bg-violet-700 transition-colors text-sm")
+        "Submit"))
+    (div
+      :id "ref-params-result"
+      (~tw :tokens "p-3 rounded bg-stone-100 text-stone-400 text-sm")
+      "Only 'name' will be sent — 'secret' is filtered by sx-params.")))