Improve drag interaction for entities

Currently, entities can only be moved using the small top-left handler. This feels restrictive. Allow users to drag and move entities by grabbing the entire header area for better usability.

<img width="639" height="590" alt="Image" src="https://github.com/user-attachments/assets/fae5dd7e-714d-43a5-9bcc-3e3e66993f04" />