Implement serialization/deserialization and persistent storage across services

- Add serialize/deserialize support for core models
- Add file-based load/save functions in management services
- Introduce FileManager, Config, Utility and helper utilities
- Persist observer IDs for notification services
- Resolve object relationships during load (services, bookings, invoices, job cards)
- Add controller-level loadSystemData/saveSystemData
- Load data at app startup and save on shutdown

Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/models/Service.h

@@ -1,6 +1,7 @@
 #pragma once
 #include <string>
 #include "Map.h"
+#include "Vector.h"
 #include "Enums.h"
 
 class InventoryItem;
@@ -11,14 +12,17 @@ private:
     static int m_uid;
     std::string m_id;
     std::string m_name;
+    util::Vector<std::string> m_requiredInventoryItemIDs;
     util::Map<std::string, InventoryItem*> m_requiredInventoryItems;
     double m_laborCost;
     util::State m_status;
 public:
     Service();
     Service(const std::string& name, const util::Map<std::string, InventoryItem*>& requiredInventoryItems, double laborCost);
+    Service(const std::string& id, const std::string& name, const util::Vector<std::string>& requiredInventoryItemIDs, double laborCost, util::State state);
     const std::string& getId() const;
     const std::string& getName() const;
+    const util::Vector<std::string>& getRequiredInventoryItemIDs() const;
     const util::Map<std::string, InventoryItem*>& getRequiredInventoryItems() const;
     double getLaborCost() const;
     util::State getState() const;
@@ -27,4 +31,7 @@ public:
     void setRequiredInventoryItems(const util::Map<std::string, InventoryItem*>& requiredInventoryItems);
     void setLaborCost(double laborCost);
     void setState(util::State status);
+    std::string serialize() const;
+    static Service* deserialize(const std::string&);
+    static std::string getHeaders();
 };