feat: add link to SQL-RL repository in playground.html for easy access

server/playground.html

@@ -232,6 +232,7 @@
         <h1>SQL data analyst playground</h1>
       </div>
       <div class="links">
+        <a href="https://code.xeze.org/Hackathons/SQL-RL" target="_blank" rel="noopener noreferrer">Repository</a>
         <a href="/docs">API docs</a>
         <a href="/health">Health</a>
       </div>