Fix PR review comments and refactor menu helper logic

Changes:
- Added name parameter to createTechnician for consistency
- Added function headers for notification-related methods in InventoryManagementService
- Used variables for notification title and message instead of passing strings directly
- Fixed payment reminder notification message formatting
- Moved common helper functions to MenuHelper.h
- Updated CustomerMenu to use shared helper functions instead of duplicate code
- Added missing includes in MenuHelper.h
- Removed redundant helper code from CustomerMenu.cpp
- Minor formatting and comment cleanup

Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/services/PaymentManagementService.cpp

@@ -19,7 +19,6 @@ Date: 20-May-2026
 #include "User.h"
 #include "Utility.h"
 
-
 util::Map<std::string, User*> PaymentManagementService::m_observers{};
 
 /*
@@ -128,9 +127,9 @@ void PaymentManagementService::sendPaymentReminders()
 					User* customer = serviceBooking->getCustomer();
 					if (customer)
 					{
-						sendNotification(customer,
-							"Payment Reminder",
-							"Your payment for Invoice ID " + invoice->getId() + " is still pending.Please complete the payment." + invoice->getId());
+						std::string title = "Payment Reminder";
+						std::string message = "Your payment for Invoice ID " + invoice->getId() + " is still pending. Please complete the payment.";
+						sendNotification(customer, title, message);
 					}
 				}
 			}