Add rendered launch demo media

[SonAIengine]

Summary

• add the rendered Synaptic Memory launch demo MP4 and GIF
• add docs/launch/render_demo_video.py to regenerate the media on this server with ffmpeg
• update launch docs/playbook to point to the generated assets

Verification

• uv run ruff check .
• uv run python docs/launch/render_demo_video.py --mp4-only
• ffprobe: h264, 1280x720, 30fps, 22.6s
• visual frame spot-check of start/middle/end frames
• git diff --check