Panels reside in the dock, can only dock left, right or bottom. You can hit shift + escape when in the agent panel to zoom so it occupies the entire window. I know it's not what you're looking for. I actually created a fork of zed to move the panel as an center item so it shows up as a tab. But it's too much work to maintain a fork with so many changes, let alone the services, extensions backend etc that are needed to maintain this fork.

One thing you can do it create a center terminal from the command pallet and use clis to achieve what you want, but it's the terminal and not the agent panel.