feat: build registry for chat-ui

[thucpn]

Follow guide: https://ui.shadcn.com/docs/registry/getting-started

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[thucpn]

Generates the registry JSON files in the public/r directory. We can host it to a domain.
Then user can install it like:

npx shadcn@latest add `<PUBLIC_URL>/r/chat-section.json`

We can also use github raw url, eg:

npx shadcn@latest add https://raw.githubusercontent.com/run-llama/chat-ui/refs/heads/tp/build-registry/apps/web/public/r/chat-section.json

[thucpn]

Should replace url when we deploy it somewhere