feat: add multiple build output formats (ES/CJS/UMD)

[UmbraCi]

Summary

This PR adds support for multiple build output formats to better serve different use cases.

Changes

• Configure Rollup to generate three output formats:
  • ES Module () - for modern bundlers with tree-shaking support
  • CommonJS () - for require/legacy toolchains
  • UMD () - for direct usage with global variables
• Update package.json:
  • Set main to CommonJS entry
  • Set module to ES Module entry
  • Add unpkg fields for CDN usage
  • Update exports field to support conditional imports
  • Add all output directories to files field
• Update .gitignore to exclude build outputs

Benefits

• Modern bundlers can use ES modules for better tree-shaking
• Legacy tools can continue using CommonJS
• CDN users can directly include UMD builds via <script> tags
• Better compatibility across different environments

Testing

• ✅ Build succeeds and generates all three formats
• ✅ All formats include source maps
• ✅ Main library and plugins are built in all formats