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/search-results.sx

@@ -0,0 +1,11 @@
+(defcomp
+  (&key items query)
+  (<>
+    (if
+      (empty? items)
+      (p
+        (~tw :tokens "p-3 text-sm text-stone-400")
+        (str "No results for \"" query "\""))
+      (map
+        (fn (item) (div (~tw :tokens "px-3 py-2 text-sm text-stone-700") item))
+        items))))