Add launch video demo script

[SonAIengine]

Summary

• add examples/launch_demo.py, a 60-second terminal demo over documents, structured ticket rows, retrieval feedback, and memory health metadata
• add generated launch media: docs/launch/synaptic-memory-demo.mp4 and docs/launch/synaptic-memory-demo.gif
• add docs/launch/render_demo_video.py to regenerate the MP4/GIF with ffmpeg on this server
• add docs/launch/demo_video.md with storyboard, captions, recording commands, generated media links, and social post copy
• connect the video asset from the promotion playbook and Show HN checklist

Verification

• uv run ruff check .
• uv run python examples/launch_demo.py --no-pause
• uv run python docs/launch/render_demo_video.py
• ffprobe MP4 metadata: h264, 1280x720, 30fps, 22.6s
• launch-doc markdown fence check
• git diff --check