refine "sites" / extensions packaging

[kfix]

the multi-chat Franz app has "recipes", very similar to MacPin sites: https://github.com/meetfranz/recipe-slack/blob/master/webview.js
https://github.com/meetfranz/plugins/blob/master/docs/integration.md

They have pulled off multi-repo sites, so maybe I could do the same?
Or just move sites/ to a submodule....

Or try to support the W3C WebExtensions API?

[kfix]

Oh, I really like the Franz recipes, just hate the Electron (Flash 2.0?) runtime!

https://github.com/meetfranz/franz/blob/master/src/helpers/recipe-helpers.js
https://github.com/meetfranz/franz/blob/master/src/models/Recipe.js
https://github.com/meetfranz/franz/blob/master/src/models/Service.js
https://github.com/meetfranz/franz/blob/master/src/webview/plugin.js
https://github.com/meetfranz/franz/blob/master/src/webview/lib/RecipeWebview.js

https://github.com/meetfranz/franz/blob/master/src/components/services/content/ServiceWebview.js

^ what I imagined a ReactWebView.swift might look like