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/SceneryExportTests.cs

@@ -0,0 +1,146 @@
+using StarterNG.Infrastructure.Sceneries;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class SceneryExportTests
+{
+    private static SceneryParser Parser() =>
+        new(new FixedClock(new DateTime(2026, 1, 1, 12, 0, 0)), new StubRandom());
+
+    [Fact]
+    public void An_untouched_scenery_exports_its_trainsets_back_verbatim()
+    {
+        const string scn = """
+            //$n Test
+            trainset pociag tor_1 10 0
+            node -1 -1 ep07-001 dynamic PKP/EP07 ep07 ep07.mmd 0 headdriver 0
+            endtrainset
+            FirstInit
+            """;
+        var scenery = Parser().Parse("scenery/x.scn", scn);
+
+        string exported = scenery.BuildExportContent(skipDecorTrainsets: false, new StubRandom());
+
+        Assert.DoesNotContain("{{0}}", exported);
+        Assert.Contains("trainset pociag tor_1", exported);
+        Assert.Contains("endtrainset", exported);
+    }
+
+    [Fact]
+    public void Selected_optional_includes_are_written_back_before_FirstInit()
+    {
+        const string scn = """
+            include zima.inc end //$optional 1, Zima
+            x
+            endoptional
+            FirstInit
+            """;
+        var scenery = Parser().Parse("scenery/x.scn", scn);
+
+        string exported = scenery.BuildExportContent(skipDecorTrainsets: false, new StubRandom());
+
+        Assert.Contains("include zima.inc end", exported);
+        Assert.True(exported.IndexOf("include zima.inc", StringComparison.Ordinal) <
+                    exported.IndexOf("FirstInit", StringComparison.Ordinal));
+    }
+
+    [Fact]
+    public void A_deselected_optional_include_stays_out()
+    {
+        const string scn = """
+            include zima.inc end //$optional 1, Zima
+            x
+            endoptional
+            FirstInit
+            """;
+        var scenery = Parser().Parse("scenery/x.scn", scn);
+        scenery.Includes[0].Selected = false;
+
+        string exported = scenery.BuildExportContent(skipDecorTrainsets: false, new StubRandom());
+
+        Assert.DoesNotContain("include zima.inc", exported);
+    }
+
+    [Fact]
+    public void A_kind_two_include_is_written_only_without_a_companion_timetable()
+    {
+        const string scn = """
+            include rozklad.inc end //$optional 2, Rozkład
+            x
+            endoptional
+            FirstInit
+            """;
+        var scenery = Parser().Parse("scenery/x.scn", scn);
+
+        scenery.HasCompanionTimetable = false;
+        Assert.Contains("include rozklad.inc",
+                        scenery.BuildExportContent(skipDecorTrainsets: false, new StubRandom()));
+
+        scenery.HasCompanionTimetable = true;
+        Assert.DoesNotContain("include rozklad.inc",
+                              scenery.BuildExportContent(skipDecorTrainsets: false, new StubRandom()));
+    }
+
+    [Fact]
+    public void Edited_weather_replaces_the_authored_config_block()
+    {
+        const string scn = """
+            config
+            movelight 100
+            scenario.weather.temperature 5
+            eventlauncher.range 200
+            endconfig
+            atmo 0 0 0 10 2000 0 0 0 0 endatmo
+            time 8:30 0 0 endtime
+            FirstInit
+            """;
+        var scenery = Parser().Parse("scenery/x.scn", scn);
+
+        scenery.Weather.Day = 200;
+        scenery.Weather.Temperature = 25;
+        scenery.Weather.Dirty = true;
+
+        string exported = scenery.BuildExportContent(skipDecorTrainsets: false, new StubRandom());
+
+        Assert.Contains("movelight 200", exported);
+        Assert.Contains("scenario.weather.temperature 25", exported);
+        Assert.DoesNotContain("movelight 100", exported);
+        // Config the scenery author wrote and the starter does not manage survives.
+        Assert.Contains("eventlauncher.range 200", exported);
+    }
+
+    [Fact]
+    public void Decor_trainsets_can_be_dropped_from_the_export()
+    {
+        const string scn = """
+            //$n Test
+            trainset ai_1 tor_1 10 0 //$decor
+            node -1 -1 ai-1 dynamic PKP/EP07 ep07 ep07.mmd 0 nobody 0
+            endtrainset
+            FirstInit
+            """;
+        var scenery = Parser().Parse("scenery/x.scn", scn);
+
+        Assert.True(scenery.Trainsets[0].Decor);
+        Assert.DoesNotContain("trainset ai_1",
+                              scenery.BuildExportContent(skipDecorTrainsets: true, new StubRandom()));
+        Assert.Contains("trainset ai_1",
+                        scenery.BuildExportContent(skipDecorTrainsets: false, new StubRandom()));
+    }
+
+    [Fact]
+    public void Loose_vehicles_are_appended_as_nodes_again()
+    {
+        const string scn = """
+            node -1 -1 wagon_1 dynamic PKP/111A 111a 111a.mmd none 0 nobody 0 enddynamic
+            FirstInit
+            """;
+        var scenery = Parser().Parse("scenery/x.scn", scn);
+
+        string exported = scenery.BuildExportContent(skipDecorTrainsets: false, new StubRandom());
+
+        Assert.Contains("wagon_1", exported);
+        Assert.Contains("enddynamic", exported);
+    }
+}