Till_Buettner 's screenshot above has a highlight colored over the archive option. When you create/edit an environment, there's a toggle to create an archive. If you don't see that on your environments, please let us know the property name/environment name where the archive option isn't showing up (you can also just copy/paste the URL from the environment page) and we'll take a look.
A debug library is an unminified library. If "Include Debug Library" is on, then unminified builds will be produced and deployed alongside your minified Launch files. You can find them by removing the ".min" from your embed code URL.
If you create an archive, you can download it as soon as you produce a build. So if you want to grab it from Dev, just use the archive option on your Dev environment, once you build to Dev, you can go hit the download link on your dev environment to grab the file.