Fix MQTT entry task link for project application

Updated the link for the entry task in the application instructions.

Author: wslany

pages/development/google-summer-of-code/2026.md

@@ -60,7 +60,7 @@ Broker/TLS/auth/client-id are configured globally in app settings, and connect/s
 
 Ensure reliability (reconnect/offline handling) and strong automated tests for core logic (especially topic-filter matching and message routing). 
 
-To apply for this project idea, please complete <a target="_blank" href="">this entry task</a> and include the links to the requested demo artifact in your application.
+To apply for this project idea, please complete <a target="_blank" href="https://docs.google.com/document/d/1jw87hf8iq5DStlKOhT9yvQP7trsnzgZ6jYcH99BxBMs/edit?usp=sharing">this entry task</a> and include the links to the requested demo artifact in your application.
 
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