feat(react): enable automatic CSS injection for MediaSkinDefault component

- Configure rollup to inject CSS directly into JavaScript bundles instead of extracting to separate files
- Remove CSS export from package.json as styles are now auto-included
- Update react-demo to remove manual CSS import requirement
- Enable seamless component usage: import { MediaSkinDefault } from '@vjs-10/react' now automatically includes styles

This provides the expected developer experience for React component libraries where
importing a component automatically brings its required styles without manual CSS imports.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

examples/react-demo/src/main.tsx

@@ -1,7 +1,6 @@
 import React from 'react';
 import ReactDOM from 'react-dom/client';
 import { MediaProvider, Video, MediaSkinDefault } from '@vjs-10/react';
-import '@vjs-10/react/style.css';
 
 const DemoPlayer = () => {
   return (