docs: add live demo link near the top of the README

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

Author: jxxyx-bloop

README.md

@@ -2,6 +2,10 @@
 
 A collaborative farewell card where your whole team can pin sticky-note goodbyes on a shared board — synced live for everyone, deployed on free hosting in minutes.
 
+### ▶️ [**Try the live demo →**](https://farewell-card.jiayilee.workers.dev/)
+
+See a real deployed card in action before you make your own.
+
 > ⭐ **If this helps you say a nice goodbye, please star the repo** — it's the easiest way to say thanks and helps other teams find it.
 
 | 🍊 Original theme | 🏖️ Beach theme |