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/InventoryItem.cpp

@@ -1,3 +1,7 @@
+#include <sstream>
+#include <stdexcept>
+#include "Factory.h"
+#include "StringHelper.h"
 #include "InventoryItem.h"
 
 int InventoryItem::m_uid = 0;
@@ -15,6 +19,20 @@ InventoryItem::InventoryItem(const std::string& partName, int quantity, double p
     m_status(util::State::ACTIVE),
     m_price(price) {}
 
+InventoryItem::InventoryItem(const std::string& id, const std::string& partName, int quantity, double price, util::State status)
+    : m_id(id),
+    m_partName(partName),
+    m_quantity(quantity),
+    m_status(status),
+    m_price(price)
+{
+    int idNumber = util::extractNumber(m_id);
+    if (idNumber > m_uid)
+    {
+        m_uid = idNumber;
+    }
+}
+
 const std::string& InventoryItem::getId() const
 {
     return m_id;
@@ -63,4 +81,51 @@ void InventoryItem::setPrice(double price)
 void InventoryItem::setState(util::State status)
 {
     m_status = status;
-}
+}
+
+std::string InventoryItem::serialize() const
+{
+    std::ostringstream serializedInventoryItem;
+    serializedInventoryItem << m_id << ','
+        << m_partName << ','
+        << m_quantity << ','
+        << m_price << ','
+        << util::getStateString(m_status);
+    return serializedInventoryItem.str();
+}
+
+InventoryItem* InventoryItem::deserialize(const std::string& record)
+{
+    std::string id, partName;
+    std::string quantityString, priceString, statusString;
+    int quantity;
+    double price;
+    std::istringstream serializedInventoryItem(record);
+    getline(serializedInventoryItem, id, ',');
+    getline(serializedInventoryItem, partName, ',');
+    getline(serializedInventoryItem, quantityString, ',');
+    getline(serializedInventoryItem, priceString, ',');
+    getline(serializedInventoryItem, statusString, ',');
+    try
+    {
+        quantity = std::stoi(quantityString);
+        price = std::stod(priceString);
+    }
+    catch (...)
+    {
+        throw std::runtime_error("Invalid inventory item data");
+    }
+    util::State status = util::getState(statusString);
+    return Factory::getObject<InventoryItem>(
+        id,
+        partName,
+        quantity,
+        price,
+        status
+    );
+}
+
+std::string InventoryItem::getHeaders()
+{
+    return "ID,PartName,Quantity,Price,Status";
+}