v1.8.1

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1. fix: keep face mosaic locked on faces during preview and export.
2. fix: pause playback when starting video export.
3. fix: clear face mosaic scan state when importing a new video.

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1. 修复：确保人脸马赛克在预览和导出时始终跟随人脸移动。
2. 修复：开始导出视频时自动暂停播放。
3. 修复：导入新视频时清除人脸马赛克扫描状态。