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

Models/Company.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace Invoice_App.Models;
+
+public class Company
+{
+    public string CompanyName { get; set; }
+    public string? LogoPath { get; set; }
+    public string Address { get; set; }
+    public string ZipCode { get; set; }
+    public string City { get; set; }
+    public string CVR { get; set; }
+    public string PhoneNumber { get; set; }
+    public string? AccountRegistration { get; set; }
+    public string? AccountNumber { get; set; }
+    
+}

Models/Customer.cs

@@ -0,0 +1,11 @@
+namespace Invoice_App.Models;
+
+public class Customer
+{
+    public string Name { get; set; }
+    public string Address { get; set; }
+    public string? ZipCode { get; set; }
+    public string? City { get; set; }
+    public string? PhoneNumber { get; set; }
+    public string? Email { get; set; }
+}

Models/Vehicle.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace Invoice_App.Models;
+
+public class Vehicle
+{
+	public string? Make { get; set; }
+	public string? Model { get; set; }
+	public DateTime? RegistrationDate { get; set; }
+	public string? VinNumber { get; set; }
+	public decimal? Kilometers { get; set; }
+	public string? Comments { get; set; }
+}

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()
+    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();
+
 }