feat: link Tertiary Infotech Academy to website in footer

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: alfredang

index.html

@@ -110,7 +110,7 @@ <h3>Edit Question</h3>
      or use the local dev server script below
 -->
 <footer class="site-footer">
-  Powered by Tertiary Infotech Academy Pte Ltd
+  Powered by <a href="https://www.tertiarycourses.com.sg/" target="_blank" rel="noopener noreferrer">Tertiary Infotech Academy Pte Ltd</a>
 </footer>
 
 <script src="firebase-config.js"></script>