feat: add RN_GET_INDEX event and auto host detection

[dannyhw]

What I did

Auto WebSocket Host Detection

• Added websockets: 'auto' option in metro config that automatically detects the local IP address
• The getLocalIPAddress() function finds the machine's IPv4 address from network interfaces
• Eliminates the need to manually configure host/port for device connections

RN_GET_INDEX Event

• Added RN_GET_INDEX channel event that clients can send to request the story index
• Server responds with RN_INDEX_RESPONSE containing the current story index
• Enables external tooling (VS Code extension, dev tools) to query available stories

Build-time WebSocket Config Injection

• New STORYBOOK_WEBSOCKET global variable injected into storybook.requires at build time
• Contains { host, port } configuration determined during metro bundling
• View.tsx now reads from this global when host/port params are not explicitly provided

Other Changes

• Added --host and --port CLI arguments to the generate script
• Added WebSocket ping interval (10s) to keep connections alive
• Standardized on globalThis instead of global
• Added test script (scripts/test-ws.ts) for testing WebSocket connection

How to test

1. In metro config, set websockets: 'auto':

module.exports = withStorybook(defaultConfig, {
  enabled: true,
  websockets: 'auto',
});

2. Run the app on a physical device - it should auto-connect to the WebSocket server

3. Test the RN_GET_INDEX event using the test script:

cd examples/expo-example
npx ts-node scripts/test-ws.ts <host> <port>