Баланс вокала и инструментала

# 1) Request a presigned URL → returns { uploadUrl, storageKey }
curl -X POST 'https://api.elysiatools.com/api/upload/presign/audio-vocal-instrumental-balance' \
  -H 'Content-Type: application/json' \
  -d '{"filename":"audioFile.ext","contentType":"application/octet-stream","size":12345}'
curl -X POST 'https://api.elysiatools.com/api/upload/presign/audio-vocal-instrumental-balance' \
  -H 'Content-Type: application/json' \
  -d '{"filename":"vocalFile.ext","contentType":"application/octet-stream","size":12345}'
curl -X POST 'https://api.elysiatools.com/api/upload/presign/audio-vocal-instrumental-balance' \
  -H 'Content-Type: application/json' \
  -d '{"filename":"instrumentalFile.ext","contentType":"application/octet-stream","size":12345}'

# 2) PUT the file bytes directly to the presigned uploadUrl
curl -X PUT '<presigned uploadUrl>' \
  --data-binary @/path/to/file.ext

# 3) Call the tool, passing the returned storageKey for each file field
curl -X POST 'https://api.elysiatools.com/ru/api/tools/audio-vocal-instrumental-balance' \
  -F 'audioFile=uploads/2026/01/01/your-tool-1700000000000-abc123.ext' \
  -F 'vocalFile=tests/fixtures/audio-to-text-transcriber-english.flac' \
  -F 'instrumentalFile=tests/fixtures/audio-to-text-transcriber-english.flac' \
  -F 'sourceMode=stems' \
  -F 'vocalOffsetDb=3' \
  -F 'normalizeFinalLoudness=false' \
  -F 'targetLufs=-16' \
  -F 'outputFormat=mp3'