Added classes for Company, Customer, and Vehicle. Also added test for Vehicle class

Program.cs

@@ -1,5 +1,6 @@
 using Avalonia;
 using System;
+using Invoice_App.Models;
 
 namespace Invoice_App;
 
@@ -9,8 +10,28 @@ class Program
     // SynchronizationContext-reliant code before AppMain is called: things aren't initialized
     // yet and stuff might break.
     [STAThread]
-    public static void Main(string[] args) => BuildAvaloniaApp()
-        .StartWithClassicDesktopLifetime(args);
+    public static void Main(string[] args)
+	{
+		
+		TestVehicleClass();
+
+		BuildAvaloniaApp()
+			.StartWithClassicDesktopLifetime(args);
+	} 
+
+
+	private static void TestVehicleClass()
+	{
+	    var testCar = new Vehicle();
+	    testCar.Make = "BMW";
+	    testCar.Model = "320i";
+	    testCar.VinNumber = "ABC123";
+	    testCar.Kilometers = 50000;
+	    testCar.RegistrationDate = DateTime.Now;
+	    testCar.Comments = "Good condition";
+	    
+	    // No console output for now - just creating the object to test compilation
+	}
 
     // Avalonia configuration, don't remove; also used by visual designer.
     public static AppBuilder BuildAvaloniaApp()
@@ -18,4 +39,5 @@ class Program
             .UsePlatformDetect()
             .WithInterFont()
             .LogToTrace();
+
 }