Make Scenery a domain aggregate with no I/O

Parsing and loading move to Infrastructure/Sceneries. Weather becomes a value
object owning the "does this differ from the file" rule.

StarterNG.Tests/SceneryRepositoryTests.cs

@@ -0,0 +1,101 @@
+using System.Text;
+using StarterNG.Infrastructure.Adapters;
+using StarterNG.Infrastructure.Sceneries;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class SceneryRepositoryTests
+{
+    private static SceneryRepository Build(InMemoryFileSystem files, out FileDiagnosticsLog log)
+    {
+        var paths = new GamePaths("game");
+        var clock = new FixedClock(new DateTime(2026, 1, 1));
+        log = new FileDiagnosticsLog(files, clock, paths);
+        return new SceneryRepository(files, paths, log, new SceneryParser(clock, new StubRandom()));
+    }
+
+    [Fact]
+    public void Every_scn_in_the_scenery_folder_is_loaded()
+    {
+        var files = new InMemoryFileSystem()
+            .WithFile(Path.Combine("game", "scenery", "kato.scn"), "//$n Katowice")
+            .WithFile(Path.Combine("game", "scenery", "gdansk.scn"), "//$n Gdańsk");
+
+        var loaded = Build(files, out _).LoadAll();
+
+        Assert.Equal(2, loaded.Count);
+        Assert.Contains(loaded, scenery => scenery.Name == "Katowice");
+    }
+
+    [Fact]
+    public void Authoring_scratch_files_and_other_extensions_are_skipped()
+    {
+        var files = new InMemoryFileSystem()
+            .WithFile(Path.Combine("game", "scenery", "$wip.scn"), "//$n Robocza")
+            .WithFile(Path.Combine("game", "scenery", "kato.inc"), "//$n Include")
+            .WithFile(Path.Combine("game", "scenery", "kato.scn"), "//$n Katowice");
+
+        var loaded = Build(files, out _).LoadAll();
+
+        Assert.Equal("Katowice", Assert.Single(loaded).Name);
+    }
+
+    [Fact]
+    public void A_companion_sbt_is_noticed_when_the_scenery_is_loaded()
+    {
+        var files = new InMemoryFileSystem()
+            .WithFile(Path.Combine("game", "scenery", "kato.scn"), "//$n Katowice")
+            .WithFile(Path.Combine("game", "scenery", "kato.sbt"), "timetable");
+
+        var scenery = Assert.Single(Build(files, out _).LoadAll());
+
+        Assert.True(scenery.HasCompanionTimetable);
+    }
+
+    [Fact]
+    public void A_missing_scenery_loads_as_null_rather_than_throwing()
+    {
+        Assert.Null(Build(new InMemoryFileSystem(), out _).Load(Path.Combine("game", "scenery", "gone.scn")));
+    }
+
+    [Fact]
+    public void Progress_is_reported_once_per_file()
+    {
+        var files = new InMemoryFileSystem()
+            .WithFile(Path.Combine("game", "scenery", "a.scn"), "//$n A")
+            .WithFile(Path.Combine("game", "scenery", "b.scn"), "//$n B");
+        var steps = new List<int>();
+
+        Build(files, out _).LoadAll(new Progress<StarterNG.Application.Abstractions.SceneryLoadProgress>(
+            step => { lock (steps) steps.Add(step.Loaded); }));
+
+        // Progress<T> posts asynchronously; give it a moment to drain.
+        SpinWait.SpinUntil(() => { lock (steps) return steps.Count == 2; }, TimeSpan.FromSeconds(2));
+        lock (steps)
+            Assert.Equal(new[] { 1, 2 }, steps.OrderBy(value => value));
+    }
+
+    [Fact]
+    public void The_preview_image_is_found_next_to_the_scenery()
+    {
+        var files = new InMemoryFileSystem()
+            .WithFile(Path.Combine("game", "scenery", "kato.scn"), "//$i kato.jpg")
+            .WithFile(Path.Combine("game", "scenery", "images", "kato.jpg"), "binary");
+        var scenery = Assert.Single(Build(files, out _).LoadAll());
+
+        string? image = new SceneryImageLocator(files).Resolve(scenery);
+
+        Assert.Equal(Path.Combine("game", "scenery", "images", "kato.jpg"), image);
+    }
+
+    [Fact]
+    public void A_scenery_without_an_image_directive_resolves_to_nothing()
+    {
+        var files = new InMemoryFileSystem()
+            .WithFile(Path.Combine("game", "scenery", "kato.scn"), "//$n Katowice");
+        var scenery = Assert.Single(Build(files, out _).LoadAll());
+
+        Assert.Null(new SceneryImageLocator(files).Resolve(scenery));
+    }
+}