fix(render): A7 Fix D D-2 — EnvCell shell binds its own per-cell light set (#140)

The cell shell read whatever light set (SSBO 4/5) WbDrawDispatcher last left
bound, lighting walls with a leaked set. EnvCellRenderer now uploads its own
binding=4 global lights (frame PointSnapshot via GlobalLightPacker) + a binding=5
per-instance set, computed per cell by LightManager.SelectForObject over the
cell's world bounds (mirrors _cellIdToSlot + WbDrawDispatcher.ComputeEntityLightSet).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -7775,6 +7775,7 @@ public sealed class GameWindow : IDisposable
             // SceneLighting UBO built below (binding=1) — terrain/sky read those.
             Lighting.BuildPointLightSnapshot(camPos);
             _wbDrawDispatcher?.SetSceneLights(Lighting.PointSnapshot);
+            _envCellRenderer?.SetPointSnapshot(Lighting.PointSnapshot);   // A7 Fix D (D-2)
 
             var ubo = AcDream.Core.Lighting.SceneLightingUbo.Build(
                 Lighting, in atmo, camPos, (float)WorldTime.DayFraction);