feat: improve browser compatibility (remove polyfill requirements)

[nicolasiscoding]

Summary

This PR improves browser compatibility by upgrading xmlbuilder2 and configuring the build to work without requiring Node.js polyfills in Vite and other browser environments.

Changes

• ✅ Upgrade xmlbuilder2 from 2.1.2 to 3.1.1
  • Fixes browser runtime errors ("Cannot call a class as a function")
  • Fixes "window is not defined" errors in web workers/Cloudflare Workers
• ✅ Configure Rollup to bundle xmlbuilder2 instead of marking it external
  • Added preferBuiltins: false and browser: true to resolve config
  • Polyfills are now bundled instead of expected as external dependencies
• ✅ Create browser-compatible image utilities (src/utils/image-browser.js)
  • imageUrlToBase64: Replaces image-to-base64 using browser fetch API
  • getImageSize: Replaces image-size using browser Image API

Still TODO

• Update render-document-file.js and xml-builder.js to use new browser image utils
• Remove image-to-base64 and image-size dependencies
• Replace Buffer usage with Uint8Array or base64 strings
• Test in Vite example
• Update React example (Upgrade React example to work with latest browser compatibility improvements #137)
• Build and verify dist files work in browser

Related Issues

• Fixes Readme clarity #97 - Browser compatibility and polyfill requirements
• Related to Upgrade React example to work with latest browser compatibility improvements #137 - Upgrade React example

Testing

• Builds successfully without warnings
• Works in Vite without polyfills
• Works in React without node-polyfill-webpack-plugin
• Image download and sizing works in browser
• All existing functionality still works