added statup with Windows feature

CursorLang/Services/IStartupService.cs

@@ -0,0 +1,18 @@
+using CursorLang.Models;
+
+namespace CursorLang.Services;
+
+/// <summary>
+/// Starting the app together with Windows.
+/// </summary>
+public interface IStartupService
+{
+    /// <summary>Finds out the current state of startup.</summary>
+    Task<StartupState> GetStateAsync();
+
+    /// <summary>
+    /// Asks for startup to be switched on or off and answers with the state that
+    /// came of it: the request to switch it on may well be turned down.
+    /// </summary>
+    Task<StartupState> SetEnabledAsync(bool enabled);
+}