修复生成确认与素材导出

补齐外部生成确认请求的 JSON Content-Type

本地屏蔽已确认终态任务避免轮询重复弹窗

单素材导出改为读取 Blob 后触发浏览器下载

序列帧导出按 frame objectKey 换签读取

src/components/image-editor/ImageCanvasExportModel.ts

@@ -207,6 +207,7 @@ export async function readLayerImageSequenceFrameBlob(
 ) {
   return readAssetSourceBlob({
     source: frame.imageSrc,
+    objectKey: frame.objectKey,
     refreshKey: `${layer.taskId ?? layer.resourceId}:${frame.frameIndex}`,
   });
 }