Major refactoring for game objects

src/items/ItemRegistry.h

@@ -0,0 +1,23 @@
+#pragma once
+#include <string>
+#include <unordered_map>
+#include "Item.h"
+
+namespace ZL {
+
+class ItemRegistry {
+public:
+    static ItemRegistry& instance();
+
+    void loadFromJson(const std::string& jsonPath, const std::string& zipPath = "");
+
+    // Returns nullptr if not found.
+    const Item* findById(const std::string& id) const;
+
+private:
+    ItemRegistry() = default;
+
+    std::unordered_map<std::string, Item> items_;
+};
+
+} // namespace ZL