修复模型查看器环境贴图失败时的显存泄漏

- RoomEnvironment 建好之后若 PMREM 生成失败，原先只把引用置空，它的几何与贴图不会释放
- 失败分支改为先释放已建出的 RoomEnvironment，再释放可能已建出的 PMREMGenerator

packages/model3d-viewer/src/scene.ts

@@ -250,7 +250,12 @@ export async function createModel3dViewerScene(
     scene.environmentIntensity = ENVIRONMENT_INTENSITY;
   } catch {
     // 环境贴图只影响材质观感，取不到时退化为纯光照渲染。
-    roomEnvironment = null;
+    if (roomEnvironment) {
+      disposeModel3dViewerObject(roomEnvironment);
+      roomEnvironment = null;
+    }
+    pmremGenerator?.dispose();
+    pmremGenerator = null;
   }
 
   abortIfNeeded();