Dock separators support

Currently, Glow is not able to customize the dock separators and shows a blank space in their place

Default: <img width="140" height="83" alt="Image" src="https://github.com/user-attachments/assets/0dfbc9fb-e430-414a-a938-6b32bfcd8f44" />
Glow: <img width="140" height="83" alt="Image" src="https://github.com/user-attachments/assets/81c3755f-a777-41d1-95d8-32851530c4cd" />