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

src/lib/config/UnlocksConfig.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+// A single [[unlock]] entry from unlocks.toml — an unlock group, the unit of
+// loot awarded by defence station drops (REQ-DEF-SCHEMATIC-DROP,
+// REQ-LOCK-EXPLICIT). Awarding a group unlocks all of its granted members at
+// once. Anything not granted by any group is available from game start.
+struct UnlockGroupDef
+{
+    std::string id;                              // Unique unlock-group id.
+    int stationLevel;                            // Min destroyed station level to become eligible.
+    std::vector<std::string> requiredGroupIds;   // Prerequisite unlock-group ids (REQ-LOCK-PREREQ).
+
+    // Granted ids by kind (each defaults to empty; a group grants >= 1 item).
+    std::vector<std::string> ships;
+    std::vector<std::string> modules;
+    std::vector<std::string> buildings;
+    std::vector<std::string> recipes;            // Assembler recipe ids only.
+};
+
+struct UnlocksConfig
+{
+    std::vector<UnlockGroupDef> groups;
+};