An inert <hf-color-group> holds a lane's data-color-grading; <video>, <img>
and <canvas> join with data-color-group. A member's own grading overrides
its group's. The runtime discovers members, regrades them when the group's
grading or a member's data-color-group changes, and ungrades them when the
group element or its grading goes, drawing only members on screen.
Render keeps group-graded video at full size like directly graded video,
and lint accepts (and still validates) grading on hf-color-group.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
