Introduce layers, ports and a composition root

Ports in Application/Abstractions, adapters in Infrastructure, hand-wired
AppServices (no reflection, as PublishAot requires). Adds a test project.

StarterNG.Tests/InstallationCheckTests.cs

@@ -0,0 +1,39 @@
+using StarterNG.Infrastructure;
+using StarterNG.Infrastructure.Adapters;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class InstallationCheckTests
+{
+    [Fact]
+    public void An_empty_folder_reports_every_missing_game_directory()
+    {
+        var strings = new FakeStrings().With("FaultNoDir", "missing {0}");
+        var check = new InstallationCheck(new GamePaths("game"), new InMemoryFileSystem(), strings);
+
+        var faults = check.Run();
+
+        Assert.Contains("missing /dynamic", faults);
+        Assert.Contains("missing /scenery", faults);
+        Assert.Contains("FaultNoWeights", faults);
+    }
+
+    [Fact]
+    public void A_complete_installation_reports_no_missing_directories()
+    {
+        var files = new InMemoryFileSystem()
+            .WithDirectory(Path.Combine("game", "dynamic"))
+            .WithDirectory(Path.Combine("game", "sounds"))
+            .WithDirectory(Path.Combine("game", "models"))
+            .WithDirectory(Path.Combine("game", "scenery"))
+            .WithDirectory(Path.Combine("game", "textures"))
+            .WithFile(Path.Combine("game", "data", "load_weights.txt"), "");
+        var strings = new FakeStrings().With("FaultNoDir", "missing {0}");
+
+        var faults = new InstallationCheck(new GamePaths("game"), files, strings).Run();
+
+        Assert.DoesNotContain(faults, fault => fault.StartsWith("missing "));
+        Assert.DoesNotContain("FaultNoWeights", faults);
+    }
+}