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/anim-result.sx

@@ -0,0 +1,8 @@
+(defcomp
+  (&key color time)
+  (div
+    (~tw :tokens "sx-fade-in space-y-2")
+    (div
+      :class (str "p-4 rounded transition-colors duration-700 " color)
+      (p (~tw :tokens "font-medium") "Faded in!")
+      (p (~tw :tokens "text-sm mt-1") (str "Loaded at " time)))))