feat(A.5 T18): use cached WorldEntity AABB in dispatcher; populate at register

Per Phase A.5 spec §4.6 Change #2: WalkEntities's per-entity AABB
frustum cull was recomputing Position±5 per frame per entity. With
~10.7K entities (N1=4) at 240 FPS that is ~2.5M wasted Vector3
ops/sec.

Read the AABB from the WorldEntity cache (T8 schema) instead.
RefreshAabb runs lazily on AabbDirty=true. Populate at register time:

- LandblockLoader.BuildEntitiesFromInfo: RefreshAabb after each new
  WorldEntity construction (stabs + buildings). Refactored from
  inline object-initializer to named variable to enable the call.
- EntitySpawnAdapter.OnCreate: RefreshAabb after entity state init
  (position/rotation already set via the WorldEntity passed in).

Dynamic entities (NPCs, players) move every frame via direct
Position writes in GameWindow.cs. Migrated all three per-frame
write sites to SetPosition() (T8 mutator) so AabbDirty propagates:
  - line 5942: player entity render position update
  - line 6951: remote animated entity interpolated path
  - line 7279: remote animated entity landing/movement path

The lazy RefreshAabb in WalkEntities catches up on the next frame
after any SetPosition call — render thread only, no races.

Build green, 986 passed / 8 pre-existing failures unchanged.

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

src/AcDream.Core/World/LandblockLoader.cs

@@ -42,28 +42,32 @@ public static class LandblockLoader
         {
             if (!IsSupported(stab.Id))
                 continue;
-            result.Add(new WorldEntity
+            var stabEntity = new WorldEntity
             {
                 Id = nextId++,
                 SourceGfxObjOrSetupId = stab.Id,
                 Position = stab.Frame.Origin,
                 Rotation = stab.Frame.Orientation,
                 MeshRefs = Array.Empty<MeshRef>(),
-            });
+            };
+            stabEntity.RefreshAabb(); // A.5 T18: populate cached AABB at construction
+            result.Add(stabEntity);
         }
 
         foreach (var building in info.Buildings)
         {
             if (!IsSupported(building.ModelId))
                 continue;
-            result.Add(new WorldEntity
+            var buildingEntity = new WorldEntity
             {
                 Id = nextId++,
                 SourceGfxObjOrSetupId = building.ModelId,
                 Position = building.Frame.Origin,
                 Rotation = building.Frame.Orientation,
                 MeshRefs = Array.Empty<MeshRef>(),
-            });
+            };
+            buildingEntity.RefreshAabb(); // A.5 T18: populate cached AABB at construction
+            result.Add(buildingEntity);
         }
 
         return result;