Add anti-drift demo video to README hero

[gregherbe76]

Adds assets/anti-drift-demo.mp4 (1.9 MB) and embeds it in the README hero, just under the "The moment that pays for it" header.

⚠️ Caveat on GitHub video embedding

GitHub's README markdown renderer is selective about <video> tags. Videos uploaded directly into a GitHub comment / issue / release get a user-images.githubusercontent.com URL that renders inline everywhere. Videos referenced via a raw repo URL (what this PR uses) sometimes only show as a download link on github.com.

Recommended follow-up (1 minute, once this is merged):

1. Open any issue or comment on the repo
2. Drag the assets/anti-drift-demo.mp4 file into the comment box (GitHub uploads to its CDN)
3. Copy the resulting https://github.com/user-attachments/assets/... URL
4. In README.md, replace https://github.com/gregherbe76/vibe-memory/raw/main/assets/anti-drift-demo.mp4 with the CDN URL
5. Open another small PR with that swap

That gives the cleanest inline playback on every renderer.

Alternative: convert to GIF

If you want a true inline GIF (always renders, no playback controls needed):

ffmpeg -i assets/anti-drift-demo.mp4 -vf "fps=12,scale=720:-1:flags=lanczos" -loop 0 assets/anti-drift-demo.gif

Then in README: [anti-drift demo](assets/anti-drift-demo.gif). Trade-off: ~3-5× larger file, no audio, slightly choppier.

What's in this PR

• assets/anti-drift-demo.mp4 — the 30-second demo video (1.9 MB)
• README.md — <video> embed under the hero, with fallback link and the original text block kept as a textual fallback
• memory/decisions.jsonl — entry for the launch-assets addition

Validates clean (35 decisions, 0 drifts).

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Generated by Claude Code

[github-actions]

🧠 vibe-memory changes in this PR

1 new decision(s):

• convention [launch-assets] — added assets/anti-drift-demo.mp4 (1.9 MB) and embedded it in the README hero section
  • why: the 30-second anti-drift video is the core launch asset; embedding inline maximizes its visibility on the GitHub homepage
  • by: claude-code

Posted by the vibe-memory PR-comment workflow. Edit decisions/drift entries before merging if needed.