Add generative UI contract explainer

[tuanadr]

Summary

• adds an issue Written Content: What Is Generative UI? (And Why Text Output Is No Longer Enough) #7 explainer defining generative UI as a bounded component contract rather than arbitrary AI-made frontend code
• covers text limits, the model/app authority boundary, component libraries, streaming, safe actions, and when plain text remains the better output
• uses OpenUI as the concrete example of the contract model: schemas, components, OpenUI Lang, renderer, and app-owned actions

Validation

• git diff --check
• npx --yes markdownlint-cli "Articles/Generative UI Is a Contract Not a Screenshot.md" --disable MD013

Disclosure

Drafting and editing were AI-assisted. I checked the article against current OpenUI docs for component libraries, OpenUI Lang, streaming, and renderer behavior, and I am responsible for the final wording and technical accuracy.

Related: #7

[vishxrad]

Appreciate the effort you’ve put into this! The article would be even stronger with an example comparing a text-only response and a generative UI response for the same input prompt.