docs: use inline <video> with poster and fixed width for in-page play…

…back

Replace clickable poster image with <video> tag using poster attribute
and width=960 (fixed px, not %). Users can play directly without redirect.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs: update README for v1.0.7 release