fix: clear collections in setScene and apply cloned collections in test button

- setScene now clears collections to avoid stale references
- Test clone button applies cloned collections after setScene

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

packages/core/src/store/use-scene.ts

@@ -136,6 +136,7 @@ const useScene: UseSceneStore = create<SceneState>()(
           nodes: patchedNodes,
           rootNodeIds,
           dirtyNodes: new Set<AnyNodeId>(),
+          collections: {},
         })
         // Mark all nodes as dirty to trigger re-validation
         Object.values(patchedNodes).forEach((node) => {