Add src/installer-rp/ffmpeg.ts that downloads BtbN/FFmpeg-Builds
win64-gpl zip into %appdata%/.mc_custom/, extracts ffmpeg.exe out
of bin/, drops it at %appdata%/.mc_custom/ffmpeg.exe and verifies
with `ffmpeg -version`. Reuses existing extract-zip dep.
Add src/installer-rp/music.ts that spawns yt-dlp with
--extract-audio --audio-format vorbis --ffmpeg-location <ffmpeg.exe>
to produce <tempDir>/NN.ogg per track. Streams yt-dlp stdout to
the log channel and reports stderr on non-zero exit.
Wire both into the install IPC handler: step 2-1 now preps both
binaries, step 2-2 iterates the music list and downloads each
track. Track the currently running child process in state so the
cancel button can kill it instead of waiting for it to finish.
Image / zip / place steps remain stubbed.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
