js: only apply target="_blank" to IDE build

On the web, we want to be able to navigate between the various Pybricks
subdomains without opening new tabs. But Pybricks Code is treated as an
"app", we don't want links to open in Pybricks Code.

doc/common/_static/js/ide.js

@@ -1,3 +1,4 @@
+// Since Pybricks Code is an "app", all external links get opened in new tab/window
 // https://stackoverflow.com/a/62742435/1976323
 $(document).ready(function () {
     $('a[href^="http://"], a[href^="https://"]').not('a[class*=internal]').attr('target', '_blank');