I'm new to Google Apps Script, so forgive me if I use the wrong terminology. I'm trying to build a Google Apps Add-On but I'm having trouble piecing things together. Ideally I'd like to add a right-click menu to all documents when someone installs my Add-On. Similarly to how LucidChart adds a top level menu to all docs.

Once in the old editor there's "Run" menu:

that has a "Test as add-on" function:

That opens a dialog that allows you to open another document with the add-on

Before finding this out, I enabled showing the script manifest, added the "addOn" entry, and deployed as a Test Add On in the new editor. I'm not sure if that had an effect.