docs: add demo GIF to README

Author: jiwoomap

README.md

@@ -8,6 +8,10 @@
 > 🚀 **Your Personal AI Analyst with Long-term Memory.**  
 > A Dockerized dashboard that turns [TradingAgents](https://github.com/TauricResearch/TradingAgents) into a personalized trading assistant. It not only analyzes the market but also **remembers your insights via [Obsidian](https://obsidian.md).**
 
+<p align="center">
+  <img src="assets/demo.gif" alt="Demo Animation" width="100%">
+</p>
+
 <details>
 <summary>📸 <strong>Click to view Dashboard Screenshot</strong></summary>
 <p align="center">