test: stabilize Preview3D camera state assertion

Use a polling assertion before reading Preview3D camera state so the test waits for async state propagation after execution and avoids null reads in CI.

browser_tests/tests/load3d/preview3dExecution.spec.ts

@@ -109,10 +109,19 @@ test.describe('Preview3D execution flow', { tag: ['@node', '@slow'] }, () => {
     const savedPath = await pipeline.getModelFileWidgetValue(
       Preview3DPipelineContext.previewNodeId
     )
+    await expect
+      .poll(
+        () =>
+          pipeline.getCameraStateFromProperties(
+            Preview3DPipelineContext.previewNodeId
+          ),
+        { timeout: 15_000 }
+      )
+      .not.toBeNull()
+
     const savedCamera = await pipeline.getCameraStateFromProperties(
       Preview3DPipelineContext.previewNodeId
     )
-    expect(savedCamera, 'Camera state present after execution').not.toBeNull()
 
     const workflowName = `p3d-restore-${Date.now().toString(36)}`
     await pipeline.comfyPage.menu.workflowsTab.open()