GUI: Draft interface scaling for Hi-DPI needs adjustability

Reported by several users in discord that there is apparently no way to adjust the ratio of screen space devoted to packs vs picked cards:


While the ratio is pretty good for 1920x1080 screens, it is imbalanced on 2560x1440, and hopelessly wrong for 3840x1260 as shown above. None of the sliders appear to affect it.

* Preferred solution: allow user to drag to set the size of the panel
* Secondary solution: add another slider in GUI settings that controls the ratio of the panels.
* Tertiary solution: use detected screen ratio when setting the size of the panel, targeting ~50% height

I would consider this a high priority improvement.

No file, test, or entry point is named. Start by locating the Draft interface layout and the existing GUI settings or sliders that control panel sizing. Done means the packs-versus-picked-cards panel ratio can be adjusted for Hi-DPI screen sizes, preferably by dragging, with the chosen behavior covered by an appropriate test if one exists.

Written by the indexing model from the issue text.