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/inline-validation-demo.sx

@@ -0,0 +1,24 @@
+(defcomp
+  ()
+  (form
+    (~tw :tokens "space-y-4")
+    :sx-post "/sx/(geography.(hypermedia.(example.(api.validate-submit))))"
+    :sx-target "#validation-result"
+    :sx-swap "innerHTML"
+    (div
+      (label (~tw :tokens "block text-sm font-medium text-stone-700 mb-1") "Email")
+      (input
+        :type "text"
+        :name "email"
+        :placeholder "user@example.com"
+        :sx-get "/sx/(geography.(hypermedia.(example.(api.validate))))"
+        :sx-trigger "blur"
+        :sx-target "#email-feedback"
+        :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"))
+      (div :id "email-feedback" (~tw :tokens "mt-1")))
+    (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 "validation-result")))