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-event-sse-message-demo.sx

@@ -0,0 +1,18 @@
+(defcomp
+  ()
+  (div
+    (~tw :tokens "space-y-3")
+    (div
+      :sx-sse "/sx/(geography.(hypermedia.(reference.(api.sse-time))))"
+      :sx-sse-swap "time"
+      :sx-swap "innerHTML"
+      :sx-on:sx:sseMessage "var c = parseInt(document.getElementById('ref-evt-ssemsg-count').dataset.count || '0') + 1; document.getElementById('ref-evt-ssemsg-count').dataset.count = c; document.getElementById('ref-evt-ssemsg-count').textContent = c + ' messages received'"
+      (div
+        :id "ref-evt-ssemsg-output"
+        (~tw :tokens "p-3 rounded bg-stone-100 text-stone-600 text-sm font-mono")
+        "Waiting for SSE messages..."))
+    (div
+      :id "ref-evt-ssemsg-count"
+      (~tw :tokens "text-sm text-emerald-700")
+      :data-count "0"
+      "0 messages received")))