docs: add YouTube fallback link for the demo recording

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

Author: UsmanovMahmudkhan

README.md

@@ -31,8 +31,9 @@ services for messaging, search, recommendations, billing, and media delivery.
 
 <img src="docs/media/demo.gif" alt="Sejong Pulse demonstration" width="640"/>
 
-The animation above is a silent preview. For the full-resolution recording with audio,
-download **[docs/media/demo.mp4](docs/media/demo.mp4)**.
+The animation above is a silent preview. If it does not play, watch the full recording with
+audio on **[YouTube](https://youtu.be/jTY05J_sABs)**, or download
+**[docs/media/demo.mp4](docs/media/demo.mp4)**.
 
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