Tamagui App: Support Demo Data generation

[JonLatane]

Basically, port the logic of demo_data.dart to use the TypeScript gRPC client instead of the Flutter one, and fetch (or XmlHttpRequest if you wanna be fancy and show progress) in place of Dart http. 100k faces should work just as well in a browser as the Flutter implementation based on their GitHub.

This could be an interesting time to integrate ChatGPT into the chat discussions... Basically, you could replace randomized calls to the _demoReplies array with ChatGPT responses to the tree of parent comments. There's probably some ChatGPT/OpenAI API token that will need to be configured, so some UI.

Speaking of UI, it should go on the Server Configuration page (ServerDetailsScreen/server_details_screen.tsx), and appear only for Admins of course. If there's to be an OpenAI token input, it should be optional (falling back to the _demoReplies array, renamed to demoReplies since it's not Dart), and shouldn't store any OpenAI tokens anywhere outside the browser (or really in browser data storage either).