feat(render #53): wire EntityClassificationCache.InvalidateEntity at despawn

GameWindow.RemoveLiveEntityByServerGuid now invalidates the entity's
cache entry next to the existing _animatedEntities.Remove(). Fires for
DeleteObject (0xF747) and the dedup leg of ObjDescEvent (0xF625).

Adds test #15 (despawn-respawn under reused id repopulates fresh) per
spec section 7.5 — pins the audit's ObjDescEvent-as-despawn-respawn contract.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -2945,6 +2945,7 @@ public sealed class GameWindow : IDisposable
         _worldState.RemoveEntityByServerGuid(serverGuid);
         _worldGameState.RemoveById(existingEntity.Id);
         _animatedEntities.Remove(existingEntity.Id);
+        _classificationCache.InvalidateEntity(existingEntity.Id);
         _physicsEngine.ShadowObjects.Deregister(existingEntity.Id);
 
         // Dead-reckon state is keyed by SERVER guid (not local id) so we