feat(renderers): Add React Native renderer

[sivamrudram-eng]

Summary

This PR adds the first React Native implementation of the A2UI renderer, enabling A2UI-compliant agents to generate native mobile UIs on iOS and Android.

Features

Core Components

• A2UIRenderer - Main component for rendering A2UI specifications
• useA2UIStream - Hook for real-time streaming from agent servers

MVP Components (8 of 16)

Component	React Native Mapping	Status
Text	<Text>	✅
Button	<Pressable>	✅
Image	<Image>	✅
Row	<View flexDirection="row">	✅
Column	<View>	✅
Card	<View> with shadow	✅
List	<FlatList>	✅
TextField	<TextInput>	✅

Infrastructure

• JSONL stream parser for real-time updates
• Message dispatcher for A2UI protocol messages
• Surface registry and component buffer for state management
• Data binding support with BoundValue resolution
• Full TypeScript support

Usage Example

import { A2UIRenderer } from "@a2ui/react-native";

const App = () => {
  const spec = {
    surfaceId: "main",
    rootId: "root",
    components: [
      { id: "root", type: "Column", children: ["text1", "btn1"] },
      { id: "text1", type: "Text", content: "Hello A2UI!" },
      { id: "btn1", type: "Button", label: "Click me", action: "doSomething" },
    ],
  };

  return <A2UIRenderer spec={spec} onAction={handleAction} />;
};

Roadmap

• Add remaining components (Modal, Tabs, Slider, etc.)
• Add comprehensive test suite
• Publish to npm as @a2ui/react-native

Implements #428

Standalone Repository

This renderer is also available as a standalone package at:
https://github.com/sivamrudram-eng/a2ui-react-native

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