split the selection panel into one card per kind of selection

src/ui/MainWindow.h

@@ -31,6 +31,7 @@ class HeaderBar;
 class SelectionPanel;
 class BuildButtonBar;
 class BlueprintLibrary;
+class BuildingIconCache;
 class ItemIconCache;
 class QCloseEvent;
 class QResizeEvent;
@@ -92,6 +93,9 @@ private:
     // One per-item icon cache for the whole window (REQ-UI-ITEM-ICON): the header,
     // build bar, world view, and recipe dialog all rasterize the same SVGs.
     std::unique_ptr<ItemIconCache> m_itemIcons;
+    // Likewise one per-building chip cache (REQ-UI-BUILD-ICON), shared by the build bar
+    // and the selection panel's card headers (REQ-UI-SELECTION-CARD).
+    std::unique_ptr<BuildingIconCache> m_buildingIcons;
     GameWorldView*         m_gameWorldView;
     HeaderBar*             m_headerBar;
     SelectionPanel*        m_selectionPanel;