fix(O-T4): thread-safety lock in DatDatabaseWrapper + drop unused using

Code-review findings on T4:

1. Added lock(_lock) around _db.TryGet and TryGetFileBytes in
   DatDatabaseWrapper, matching WB's DefaultDatDatabase pattern.
   ObjectMeshManager.PrepareMeshDataAsync runs on the thread pool, so
   concurrent dat access through the adapter must be serialized — our
   underlying DatCollection is not documented as thread-safe.

2. Removed unused `using WorldBuilder.Shared.Models;` from WbMeshAdapter.cs
   (its only purpose was TerrainEntry, which moved to AcDream.Core in T2).

Build green; tests green (1147 passing, 8 pre-existing failures baseline).

Spec: docs/superpowers/specs/2026-05-21-phase-o-dat-path-unification-design.md

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

src/AcDream.App/Rendering/Wb/DatCollectionAdapter.cs

@@ -118,6 +118,7 @@ internal sealed class DatDatabaseWrapper : IDatDatabase
 {
     private readonly DatDatabase _db;
     private readonly ConcurrentDictionary<(Type, uint), IDBObj> _cache = new();
+    private readonly object _lock = new();
 
     public DatDatabaseWrapper(DatDatabase db)
     {
@@ -142,20 +143,33 @@ internal sealed class DatDatabaseWrapper : IDatDatabase
             return true;
         }
 
-        if (_db.TryGet<T>(fileId, out value))
+        lock (_lock)
         {
-            _cache.TryAdd((typeof(T), fileId), value);
-            return true;
+            if (_db.TryGet<T>(fileId, out value))
+            {
+                _cache.TryAdd((typeof(T), fileId), value);
+                return true;
+            }
         }
 
         return false;
     }
 
-    public bool TryGetFileBytes(uint fileId, [MaybeNullWhen(false)] out byte[] value) =>
-        _db.TryGetFileBytes(fileId, out value);
+    public bool TryGetFileBytes(uint fileId, [MaybeNullWhen(false)] out byte[] value)
+    {
+        lock (_lock)
+        {
+            return _db.TryGetFileBytes(fileId, out value);
+        }
+    }
 
-    public bool TryGetFileBytes(uint fileId, ref byte[] bytes, out int bytesRead) =>
-        _db.TryGetFileBytes(fileId, ref bytes, out bytesRead);
+    public bool TryGetFileBytes(uint fileId, ref byte[] bytes, out int bytesRead)
+    {
+        lock (_lock)
+        {
+            return _db.TryGetFileBytes(fileId, ref bytes, out bytesRead);
+        }
+    }
 
     public bool TrySave<T>(T obj, int iteration = 0) where T : IDBObj =>
         throw new NotSupportedException("DatDatabaseWrapper is read-only.");

src/AcDream.App/Rendering/Wb/WbMeshAdapter.cs

@@ -10,7 +10,6 @@ using DatReaderWriter.DBObjs;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using Silk.NET.OpenGL;
-using WorldBuilder.Shared.Models;
 using WorldBuilder.Shared.Services;
 
 namespace AcDream.App.Rendering.Wb;