Add resize handles to allow direct size editing of components. Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
- Add onChanged(callback) API for tracking page changes - Support Delete/Backspace key to delete selected component - Fix drag offset issue when moving components - Add unsaved changes tracking in editor demo - Update README documentation