Improve the UI/UX of the message pane

[rdeltour]

A couple suggestions:

• reduce the initial size to a line height, so that it appears like a status bar
• add an "expand" button (like a chevron) to increase the height to say 1/3 of the current height
• keep the draggable split line, but make it a bit thinner
• allow copy/pasting, both with the usual shortcuts, with a contextual menu, and a button to copy/paste all
• optionally, add a button to export the log to a text file

[marisademeglio]

• add aria-live to ensure screenreaders get message updates
• scroll automatically to new messages