refactor(json): migrate from nlohmann to rapidjson

Replace nlohmann::json with rapidjson across localization, hitbox manager, server world, and sensitive filter. Add json_utils helper for converting rapidjson documents to maps, and improve parse error handling.

include/Cubed/tools/json_utils.hpp

@@ -0,0 +1,8 @@
+
+#include <rapidjson/document.h>
+#include <string>
+#include <unordered_map>
+namespace Tools {
+std::unordered_map<std::string, std::string>
+doc_to_map(const rapidjson::Document& doc);
+}

include/Cubed/tools/sensitive_filter.hpp

@@ -1,11 +1,13 @@
 #pragma once
 
-#include <nlohmann/json.hpp>
+#include <rapidjson/document.h>
+#include <unordered_map>
+#include <vector>
 namespace Cubed {
 class SensitiveFilter {
 public:
     SensitiveFilter();
-    void load(const nlohmann::json& j);
+    void load(const rapidjson::Document& doc);
     std::string filter(std::string_view text);
 
 private: