[DOCS] Add demo GIF/video to README

[Sigmabrogz]

Description

Add an animated GIF or video showing AgentDBG in action to the README.

Why

A picture is worth a thousand words. A demo GIF showing:

• Real-time trace visualization
• Pause/resume functionality
• Step-through debugging
• Cost tracking

Would dramatically improve the README and help users understand the value instantly.

Suggested Approach

1. Use examples/demo_for_video.py to create a demo
2. Record with a tool like Kap or LICEcap
3. Keep it under 30 seconds
4. Optimize GIF size (< 5MB)
5. Add to README after the title

Good First Issue

Great for someone who wants to contribute without writing code!