Two Fronts: the campaign map shrinks to a small square at tablet width (820 px) #3563

At a tablet width (820x1180, shot with bun run probe two-fronts "/?war=short&side=marines&vs=ai" --size 820x1180, after picking the line-up preset), the campaign map draws as a small square, about 190 px wide. It sits low in the map area, and most of the space to the left of the panel is empty. Main does the same before the menu climb's round 2, so this is not a skin change: compare apps/two-fronts/docs/shots-2026-11-05/before-panel-tablet.jpg and now-panel-tablet.jpg.

Expected: the map fills the space between the overview list and the panel, as it does at 1280x800 and 390x844.

Found during the Two Fronts menu climb (#3546). That climb leaves the map alone, so this needs its own fix.