MDASH video v1 clean

Outputs: - Long: mdash-video-v1-clean-long-1920x1080.mp4 - Short: mdash-video-v1-clean-short-1080x1920.mp4 - Cover: cover.png - QA: qa/ - Manifest: manifest.json

Build notes: - MotionArray b-roll used across scenes. - Runway image-to-video used where project generation completed before build; MotionArray/Image 2.0 fallback used for other scenes. - Avatar Silvio Costa 2 used where available as fullscreen/PIP with proportional scale+crop/pad, no stretch. - ElevenLabs Mi Voz used for all scene narration; final audio normalized once via FFmpeg loudnorm target -16 LUFS / -1.5 dBTP.