Add real README demo GIF for AI-to-dashboard flow

[intraq-dev-ai]

Goal

Add a real README/demo GIF that shows the product flow instead of relying only on static screenshots.

Suggested flow

Ask AI question
→ SQL/evidence appears
→ chart is created
→ dashboard component is saved

Acceptance criteria

• Capture from the public source app using sample data only.
• Do not include real credentials, private data, or local user information.
• Store the optimized GIF or short web-friendly asset under docs/assets/demo/.
• Add it near the top of README.md, close to the existing hero screenshot.
• Keep file size reasonable for GitHub README loading.