Plot sizing policy is inconsistently remembered

Currently we don't remember the sizing policy when the user selects a new policy. We only remember it after switching to another plot (the policy with which the plot was generated becomes the new active policy):

https://github.com/user-attachments/assets/b0da2960-3d9b-4a67-9ea2-4824503b5d3b

We should update the active sizing policy of the plots service when the user changes it.
