A note-worthy thing I'm adding in this PR to fix an agent panel problem
is a trait method allowing to set a min-width in panels. I think some of
them—if not all—could benefit from it, because there is a certain width
these panels can get in that we just can't ensure they will work; things
will break. So we either accept that and let the user's common sense
understand that, or we don't allow them to reach that state... Surely, a
small enough _window_ size can still break things, but then it's out of
the realms of solution...

Release Notes:

- Agent: Fixed multi-line queued messages getting cut-off when the agent
panel is in full screen.
- Agent: Fixed agent panel getting auto-closed after submitting a queued
message when the panel is in full screen.
- Agent: Added a min-width to the agent panel, preventing it from
reaching a small enough width where it would be essentially unusable.