fix: migrate untranslated files

Author: lacolaco

adev-ja/src/content/events/v21.md

@@ -2,6 +2,8 @@
 
 # Angular v21: The Adventure Begins
 
+**Angular v21 is live**: check out the [v21 release blog](http://goo.gle/angular-v21-blog) to learn about all of the amazing new features coming your way.
+
 ## Save the Date November 20, 2025
 
 <docs-pill-row>