ffkit 是做什么的？
Help a user finish a local video or audio job. Chat about the outcome, propose a short plan, then run that plan with ffkit (pipeline of verbs, graph, or ffmpeg). Use when they mention a media file (mp4, mov, mkv, webm, wav, m4a, mp3, gif), footage, clip, Reel/Short/TikTok/YouTube, captions (mux or burn without libass), overlay, transcode, ffmpeg, rough cut, assembly, or an edit, export, or effect on files they have on disk. Requires ffmpeg, ffprobe, and ffkit on PATH matching this skill's versio