Add server-side test runner to /specs/testing page

Python evaluator runs test.sx at page load, results shown alongside
the browser runner. Both hosts prove the same 81 tests from the same
spec file — server on render, client on click.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sx/sxc/pages/docs.sx

@@ -342,7 +342,8 @@
               :source (read-spec-file (get item "filename"))))
         extension-spec-items))
     "testing" (~spec-testing-content
-      :spec-source (read-spec-file "test.sx"))
+      :spec-source (read-spec-file "test.sx")
+      :server-results (run-spec-tests))
     :else (let ((spec (find-spec slug)))
       (if spec
         (~spec-detail-content