docs: add dashboard demo video to README

Adds a ~36s screen recording of the Streamlit dashboard (portfolio &
option positions, per-persona overnight theses, AI Investment Committee
verdicts, orders, agent roster) as docs/demo.mp4, with an inline GIF
teaser at the top of the README linking to the full MP4.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -1,5 +1,11 @@
 # Overnight Local-LLM Paper-Trading Agent
 
+<p align="center">
+  <a href="docs/demo.mp4"><img src="docs/demo.gif" alt="Dashboard tour: portfolio, agent theses, AI committee verdicts, orders" width="820"></a>
+  <br>
+  <em>▶ Dashboard tour — portfolio &amp; option positions, each persona's overnight theses, the AI Investment Committee verdicts, and the orders that got placed. <a href="docs/demo.mp4">Click for the full-quality MP4 (with sound).</a></em>
+</p>
+
 Every night the Mac wakes itself, runs **4 trader personas** one at a time against **one local LLM**
 (gpt-oss-20b via [oMLX](https://omlx.ai), an Apple-MLX inference server). Each persona researches the
 web + live market data, forms up to **4 trade theses — at least one of them an options trade** —