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/home/hero.sx

@@ -0,0 +1,13 @@
+;; SX docs — home page components
+(defcomp (&key &rest children)
+  (div (~tw :tokens "max-w-4xl mx-auto px-6 py-16 text-center")
+    (h1 (~tw :tokens "text-5xl font-bold text-stone-900 mb-4")
+      (span (~tw :tokens "text-violet-600 font-mono") "(<sx>)"))
+    (p (~tw :tokens "text-2xl text-stone-600 mb-4")
+      "The framework-free reactive hypermedium")
+    (p (~tw :tokens "text-sm text-stone-400")
+      "© Giles Bradshaw 2026")
+    (p (~tw :tokens "text-lg text-stone-500 max-w-2xl mx-auto mb-12")
+      "(sx === code === data === protocol === content === behaviour === layout === style === spec === sx)")
+    (div (~tw :tokens "bg-stone-100 rounded-lg p-6 text-left font-mono text-sm mx-auto max-w-2xl")
+      (pre (~tw :tokens "leading-relaxed whitespace-pre-wrap") children))))