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/SceneryWeatherTests.cs

@@ -0,0 +1,87 @@
+using StarterNG.Domain.Sceneries;
+using StarterNG.Infrastructure.Sceneries;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class SceneryWeatherTests
+{
+    private static SceneryParser Parser(DateTime now) => new(new FixedClock(now), new StubRandom());
+
+    [Fact]
+    public void Authored_weather_is_read_from_the_config_block()
+    {
+        const string scn = """
+            config
+            movelight 172
+            scenario.weather.temperature 21.5
+            scenario.time.override 6:05
+            endconfig
+            atmo 0 0 0 50 900 0 0 0 0.7 endatmo
+            time 8:30 0 0 endtime
+            """;
+
+        var weather = Parser(new DateTime(2026, 1, 1)).Parse("scenery/x.scn", scn).Weather;
+
+        Assert.True(weather.IsAuthored);
+        Assert.Equal(172, weather.Day);
+        Assert.Equal(21.5, weather.Temperature);
+        Assert.Equal("06:05", weather.ScenarioTimeOverride);
+        Assert.Equal("08:30", weather.Time);
+        Assert.Equal(50, weather.FogStart);
+        Assert.Equal(0.7, weather.Overcast);
+    }
+
+    [Fact]
+    public void A_scenery_without_a_time_starts_at_the_players_clock()
+    {
+        var weather = Parser(new DateTime(2026, 5, 4, 17, 42, 0)).Parse("scenery/x.scn", "//$n Test").Weather;
+
+        Assert.Equal("17:42", weather.ScenarioTimeOverride);
+        Assert.False(weather.IsAuthored);
+    }
+
+    [Fact]
+    public void Freshly_parsed_weather_counts_as_unchanged()
+    {
+        var weather = Parser(new DateTime(2026, 1, 1)).Parse("scenery/x.scn", "movelight 100\n").Weather;
+
+        Assert.False(weather.Changed);
+    }
+
+    [Fact]
+    public void Editing_then_restoring_returns_to_the_authored_values()
+    {
+        var weather = Parser(new DateTime(2026, 1, 1)).Parse("scenery/x.scn", "movelight 100\n").Weather;
+
+        weather.Day = 5;
+        weather.Temperature = -12;
+        Assert.True(weather.Changed);
+
+        weather.Restore();
+
+        Assert.False(weather.Changed);
+        Assert.Equal(100, weather.Day);
+        Assert.True(weather.Dirty);
+    }
+
+    [Fact]
+    public void A_fog_range_is_clamped_into_the_supported_span()
+    {
+        var weather = new SceneryWeather();
+
+        weather.SetFogRange(start: 1, end: 999999, random: new StubRandom());
+
+        Assert.Equal(SceneryWeather.FogMin, weather.FogStart);
+        Assert.InRange(weather.FogEnd, SceneryWeather.FogMin, SceneryWeather.FogMax);
+    }
+
+    [Fact]
+    public void Random_overcast_draws_from_the_presets_rather_than_the_stored_value()
+    {
+        var weather = new SceneryWeather { Overcast = 0.42, OvercastRandom = true };
+
+        Assert.Equal(-1.5, weather.EffectiveOvercast(new StubRandom()));
+        Assert.Equal(0.42, new SceneryWeather { Overcast = 0.42 }.EffectiveOvercast(new StubRandom()));
+    }
+}