Demo GIF: the 20-second core loop at the top of the README

[tosinamuda]

User story
As a visitor skimming the README, I want a ~20-second demo of the core loop, so that I believe the product before reading a word.

Acceptance criteria

• One GIF/mp4 (<10 MB) at the top of the README showing: write → ask the agent → reviewable diff → accept → version history restore
• Recorded at realistic speed on a believable document (no lorem ipsum), readable at README width
• Asset committed (or release-hosted) so it renders on GitHub without external deps

Sub-tasks

• Shot list (draft below) agreed
• Record on the live app (human hands — staged speed reads fake)
• Trim + optimize (gifski/ffmpeg) under 10 MB
• Embed at the top of the README

Shot list (draft)

1. A real note open (thesis-like content), type one sentence
2. Select a paragraph → "Ask assistant" → short instruction ("tighten this")
3. Reply streams; file-operation card appears
4. Review diff → accept
5. Open version history → restore the previous version → close