Replace the REQ-video-ring-buffer bullet to bind the new getDisplayMedia + offscreen-document acquisition path and drop the 'active-tab' wording (the new API is screen/window-scoped, not tab-scoped, so there is nothing to re-attach on tab switch). Encoding, buffer window, and SPEC §10 acceptance citations are unchanged. Adds CON-display-capture-binding alongside the existing constraint bindings.