Skeletn MS Outlook web add-in

I have been coding for decades, but am new to MS Outlook add-ins. It seems that I need a we-based add-in, and I am experienced with (Angular 1.x) Js, HTML &CSS, but I just can't see how to get started. Now, I am trying to develop an MS Outlook web add-in. I want it to be an Angular 1.x JS app, ***without using MS Visual Studio***. I plan to add a button to the the message compose pane, and invoking it will start an Angular 1.x app which I have already coded & tested. Sounds simple, huh? Just drop the existing app into a web add-in skeleton - whcih I want you to provide. What am I look for is an MS Outlook web add-in (not using Visual Studio) for the message compose pane, not message read, which what most of the examples are for it should add a button to the message compose frame, which launches my app in a window beside the compose frame. I would not object to a button on the main ribbon which launches compose, with my app in the side window, but that is not "must have". When the app launches, an alert("Hello, world"); would be nice, preferably from the controller. That's all that it needs to do; I will provide the rest If I can have that, I know that I can slot my app into it. Who can make me a simple demo, which I can change to meet my requirements? I get the copyright of the code.