fix: complete retail parity stability pass

src/AcDream.Core/World/SkyState.cs

@@ -505,6 +505,15 @@ public sealed class WorldTimeService
     /// <summary>Current sky lighting state.</summary>
     public SkyKeyframe CurrentSky => _sky.Interpolate((float)DayFraction);
 
+    /// <summary>
+    /// Interpolate this clock's active day-group provider at an explicit day
+    /// fraction without changing the clock. Retail <c>LScape::SetDay</c>
+    /// uses this distinction: the sky continues advancing normally while
+    /// landscape lighting is sampled at noon.
+    /// </summary>
+    public SkyKeyframe SkyAtDayFraction(float dayFraction) =>
+        _sky.Interpolate(dayFraction);
+
     /// <summary>Convenience: current sun direction from derived sky state.</summary>
     public Vector3 CurrentSunDirection =>
         SkyStateProvider.SunDirectionFromKeyframe(CurrentSky);