docs(vtt): [SITE-VTT-01] add bilingual guides and sprite pixel checks

test/browser/README.md

@@ -528,3 +528,7 @@ cleanup. Pixel readiness uses the existing polling deadline, not media time alon
 The first immediate-pixel WebKit failure remains in the refactor evidence.
 This is native desktop media playback, not physical audibility or full devices.
 `document-site.spec.js` also checks generated guide links and Run Code parameters.
+
+## VTT Thumbnail documentation examples
+
+yarn test:browser document-vtt.spec.js document-site.spec.js --workers=1 validates both generated guides and their Run Code destinations after yarn build:docs. The guide test requires the original demo verbatim, preserves the original demo video and substitutes local VTT/SVG resources, and inspects actual preview screenshot pixels with pngjs. It covers red/blue crops from real mouse hover, inclusive endpoint selection via public setBar with a MouseEvent, a gap, destroy and a late event on both cores. It loads local dist explicitly and records its hash; this does not replace the verified installed-artifact suite, physical touch tests or full playback acceptance.