fix(demo): stop scene blocks from overlapping in the video

[yablokolabs]

Summary

• Five scenes of the demo video (vision, active, remeasure, approval, evaluation) held more content than a 1080-line frame. The centred stage grid then lay across the headline above it and the alert below it.
• scripts/check_scene_layout.mjs only compared elements with the frame edges, so it reported all ten scenes as good. It now also fails when stage content is taller than its row and when two blocks cover the same pixels.
• The scenes are reduced until all ten pass. The title tagline has clearance from the wordmark. The outro no longer shows the AWS line.
• The narration, its timing and the subtitles are not changed. The video is rendered again at the same length, 4:41.

Test Plan

• The new check failed on the five scenes before the scene changes (20 faults), and passes on all ten after them
• npm run typecheck in demo/videowright
• Full render, 16,885 frames, 281.4 s, 1920x1080 at 60 fps
• Frames extracted each 8 s from the new video and examined: no overlap
• Listen to the video one time from start to end