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/swap-positions-demo.sx

@@ -0,0 +1,32 @@
+(defcomp
+  ()
+  (div
+    (~tw :tokens "space-y-3")
+    (div
+      (~tw :tokens "flex gap-2")
+      (button
+        :sx-post "/sx/(geography.(hypermedia.(example.(api.swap-log))))?mode=beforeend"
+        :sx-target "#swap-log"
+        :sx-swap "beforeend"
+        (~tw :tokens "px-3 py-1.5 bg-violet-600 text-white rounded text-sm hover:bg-violet-700")
+        "Add to End")
+      (button
+        :sx-post "/sx/(geography.(hypermedia.(example.(api.swap-log))))?mode=afterbegin"
+        :sx-target "#swap-log"
+        :sx-swap "afterbegin"
+        (~tw :tokens "px-3 py-1.5 bg-violet-600 text-white rounded text-sm hover:bg-violet-700")
+        "Add to Start")
+      (button
+        :sx-post "/sx/(geography.(hypermedia.(example.(api.swap-log))))?mode=none"
+        :sx-target "#swap-log"
+        :sx-swap "none"
+        (~tw :tokens "px-3 py-1.5 bg-stone-600 text-white rounded text-sm hover:bg-stone-700")
+        "Silent Ping")
+      (span
+        :id "swap-counter"
+        (~tw :tokens "self-center text-sm text-stone-500")
+        "Count: 0"))
+    (div
+      :id "swap-log"
+      (~tw :tokens "border border-stone-200 rounded h-48 overflow-y-auto divide-y divide-stone-100")
+      (p (~tw :tokens "p-3 text-sm text-stone-400") "Log entries will appear here."))))