refactor(launcher): add DI, IUpdateEngine facade, and architecture tests

Co-authored-by: Cursor <cursoragent@cursor.com>

LanMountainDesktop.Tests/LauncherArchitectureTests.cs

@@ -0,0 +1,41 @@
+using System.Reflection;
+using Xunit;
+
+namespace LanMountainDesktop.Tests;
+
+public sealed class LauncherArchitectureTests
+{
+    private static readonly string LauncherAssemblyName = "LanMountainDesktop.Launcher";
+
+    [Fact]
+    public void Deployment_Update_Startup_Infrastructure_DoNotReferenceAvalonia()
+    {
+        var forbidden = new[] { "Deployment", "Update", "Startup", "Infrastructure" };
+        foreach (var nsSuffix in forbidden)
+        {
+            var types = GetLauncherTypes($"LanMountainDesktop.Launcher.{nsSuffix}");
+            var assembly = types.First().Assembly;
+            Assert.DoesNotContain(
+                assembly.GetReferencedAssemblies(),
+                a => string.Equals(a.Name, "Avalonia", StringComparison.OrdinalIgnoreCase));
+        }
+    }
+
+    [Fact]
+    public void LauncherFlowCoordinator_TypeDoesNotExist()
+    {
+        var coordinator = typeof(LanMountainDesktop.Launcher.Shell.LauncherOrchestrator).Assembly
+            .GetType("LanMountainDesktop.Launcher.Services.LauncherFlowCoordinator", throwOnError: false);
+        Assert.Null(coordinator);
+    }
+
+    private static IEnumerable<Type> GetLauncherTypes(string namespacePrefix)
+    {
+        var assembly = AppDomain.CurrentDomain.GetAssemblies()
+            .FirstOrDefault(a => string.Equals(a.GetName().Name, LauncherAssemblyName, StringComparison.OrdinalIgnoreCase))
+            ?? throw new InvalidOperationException("Launcher assembly not loaded.");
+
+        return assembly.GetTypes()
+            .Where(t => t.Namespace is not null && t.Namespace.StartsWith(namespacePrefix, StringComparison.Ordinal));
+    }
+}