New /testing/ section with 6 pages: overview (all specs), evaluator,
parser, router, renderer, and runners. Each page runs tests server-side
(Python) and offers a browser "Run tests" button (JS). Modular browser
runner (sxRunModularTests) loads framework + per-spec sources from DOM.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
sx-browser.js evaluates test.sx directly in the browser — click
"Run 81 tests" to see SX test itself. Uses the same Sx global that
rendered the page.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>