Update documentation for v0.3.0

- Add breaking changes warning section
- Add "Why Blokr?" section comparing with CSS pointer-events
- Rewrite all API documentation for factory function pattern
- Add element-specific locking examples
- Add scope filtering usage examples
- Add CDN usage for ES Modules
- Add migration guide from v0.2.x
- Update limitations section
- Note UMD global name change: window.Blokr → window.blokr

Author: knowledgecode