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>
