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-indicator-demo.sx

@@ -0,0 +1,23 @@
+(defcomp
+  ()
+  (div
+    (~tw :tokens "space-y-3")
+    (div
+      (~tw :tokens "flex gap-3 items-center")
+      (button
+        :sx-get "/sx/(geography.(hypermedia.(reference.(api.slow-echo))))"
+        :sx-target "#ref-indicator-result"
+        :sx-swap "innerHTML"
+        :sx-indicator "#ref-spinner"
+        :sx-vals "{\"q\": \"hello\"}"
+        (~tw :tokens "px-4 py-2 bg-violet-600 text-white rounded hover:bg-violet-700 transition-colors text-sm")
+        "Load (slow)")
+      (span
+        :id "ref-spinner"
+        (~tw :tokens "text-violet-600 text-sm")
+        :style "display: none"
+        "Loading..."))
+    (div
+      :id "ref-indicator-result"
+      (~tw :tokens "p-3 rounded bg-stone-100 text-stone-400 text-sm")
+      "Click to load (indicator shows during request).")))