Fix Complete Payment Issue

- Added "Complete Payments" header in CustomerMenu::completePayments for clarity.
- Implemented validation to check if invoices list is empty and display appropriate message.
- Added logic to verify presence of pending invoices before proceeding with payment.
- Enhanced error handling to show "Payment failed" with pressEnter prompt when no invoice is selected.
- Updated selectInvoiceFromUserForPayment in MenuHelper.h:
  - Changed function to inline and added util::clear() at start.
  - Updated column headers to "Technician ID" and "Technician Name" for clarity.
- Removed temporary AdminMenu.cpp file from enc_temp_folder.

Fixes #1750

Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/CustomerMenu.cpp

@@ -308,11 +308,35 @@ Returns:
 void CustomerMenu::completePayments()
 {
 	util::clear();
+    std::cout << "Complete Payments\n";
 	util::Map<std::string, const Invoice*> currentInvoices = m_controller.getInvoicesByUser();
+    if (currentInvoices.isEmpty())
+    {
+        std::cout << "No pending invoices available for payment.\n";
+        util::pressEnter();
+        return;
+    }
+    bool hasPending = false;
+    for (int index = 0; index < currentInvoices.getSize(); ++index)
+    {
+        const Invoice* invoice = currentInvoices.getValueAt(index);
+        if (invoice && invoice->getStatus() == util::PaymentStatus::PENDING)
+        {
+            hasPending = true;
+            break;
+        }
+    }
+    if (!hasPending)
+    {
+        std::cout << "No pending invoices available for payment.\n";
+        util::pressEnter();
+        return;
+    }
 	std::string selectedID = selectInvoiceFromUserForPayment(currentInvoices);
     if (selectedID == "")
     {
         std::cout << "Payment failed.\n";
+        util::pressEnter();
         return;
     }
     util::PaymentMode paymentMode = selectPaymentMode();