optimize-audio

Re-encode audio via ffmpeg to cut file size. Offer a few bitrate/channel options, preview them, then replace the original with the user's pick.

Preflight: ffmpeg

command -v ffmpeg >/dev/null || echo "MISSING"

If missing, stop and tell the user:

ffmpeg is required. Install it:

• macOS: brew install ffmpeg
• Ubuntu/Debian: sudo apt install ffmpeg
• Windows: winget install ffmpeg or https://ffmpeg.org/download.html

Let me know once it's installed.