split the selection panel into one card per kind of selection

src/ui/selection/BuildingTarget.h

@@ -0,0 +1,45 @@
+#pragma once
+
+#include <optional>
+#include <string>
+
+#include <QPoint>
+
+#include "BuildingId.h"
+#include "BuildingType.h"
+#include "ShipLayout.h"
+
+struct Building;
+struct ConstructionSite;
+struct SelectionContext;
+
+// One selected building id resolved to whichever of the two things it names: an
+// operational building or a construction site still queued or under construction. A
+// site carries the same configuration as the building it will become
+// (REQ-BLD-SITE-CONFIG), so the fields both have are read out here once instead of in
+// every content that shows a single building.
+struct BuildingTarget
+{
+    const Building*         building = nullptr;  // null while it is still a site
+    const ConstructionSite* site     = nullptr;  // null once it is built
+
+    BuildingType type = BuildingType::Miner;
+    std::string  recipeId;
+    std::optional<ShipLayoutConfig> shipLayout;
+    QPoint       anchor;
+
+    // False when the id names neither -- the object went away under the panel (it was
+    // deconstructed, or its site finished and its id was reused).
+    bool isValid() const { return building != nullptr || site != nullptr; }
+};
+
+// Resolves the id against the current factory state. The returned pointers are only
+// valid until the simulation next mutates, so this is called per refresh rather than
+// cached.
+BuildingTarget resolveBuildingTarget(const SelectionContext& context, BuildingId id);
+
+// The id wrapped as a construction site id when it names one, nullopt when it names an
+// operational building. Every content showing a single building hands this to
+// SelectionContent so the base can apply the site rule (REQ-UI-SELECTION-CARD).
+std::optional<BuildingId> asConstructionSite(const SelectionContext& context,
+                                            BuildingId id);