Demo: accessibility, responsive design and Playwright coverage #218

Closed as not planned along with the rest of EPIC #217: the initiative was abandoned after confirming that GitHub's /search/code endpoint doesn't include CORS headers on its actual responses (even on success), which cannot be worked around without a server-side relay — something explicitly out of scope. See #217 for the full root-cause writeup. No code was merged; this component was never implemented.