Implement config-driven unlock groups so that multiple things can be unlocked at once (including buildings)

src/test/BuildingConfigTest.cpp

@@ -1,5 +1,7 @@
 #include "catch.hpp"
 
+#include <algorithm>
+
 #include "Building.h"
 #include "BuildingConfig.h"
 #include "BuildingSystem.h"
@@ -46,7 +48,17 @@ const ShipDef* findAvailableSchematic(const GameConfig& cfg)
 {
     for (const ShipDef& def : cfg.ships.ships)
     {
-        if (def.unlockAtStationLevel == -1) { return &def; }
+        // A ship starts unlocked iff no unlock group grants it (REQ-LOCK-EXPLICIT).
+        bool granted = false;
+        for (const UnlockGroupDef& group : cfg.unlocks.groups)
+        {
+            if (std::find(group.ships.begin(), group.ships.end(), def.id) != group.ships.end())
+            {
+                granted = true;
+                break;
+            }
+        }
+        if (!granted) { return &def; }
     }
     return nullptr;
 }