Collapsible sidebar to give the video more space in windowed mode

In the Videos and Schedule tabs, the session list on the left is always
visible and cannot be hidden. In windowed mode (not fullscreen) that list
permanently reserves horizontal space, so the video player ends up narrower
than the window allows. When I want to watch a session at a larger size
without going fullscreen, there is no way to reclaim that space.

It would help to be able to collapse the sidebar so the video can use the
full width of the window, and to bring the list back when I want to choose
another session.

Environment: latest app version, current stable macOS, windowed mode.