Agent sessions: allow to resize the sessions sidebar like terminal tabs

[aiday-mar]

I wanted to increase the size of the pane chat by dragging the separator line between the panel chat and the recent sessions to the right. That separator is not expandable/contractible, so it is currently not possible to hide the recent sessions without moving the left border of the panel chat to the right. I think I would have liked the border to be movable.

[benvillalobos]

Just ran into this:

20251204-2140-35.2241395.mp4