Upload a track to SoundCloud via the API using multipart form data

Steps

1. Obtain a valid OAuth 2.1 access token for a user with upload permissions (Artist Pro / API-enabled account, depending on current access tier)
2. Send a `POST` request to the tracks endpoint with `Content-Type: multipart/form-data`, an `Authorization: OAuth <access_token>` header, and form fields for `track[title]` and the audio payload as `track[asset_data]`
3. Set additional metadata fields as needed in the same multipart body (e.g. description, sharing/privacy, genre, tags) following the track resource's writable attributes
4. Confirm the source file is in one of the accepted formats (e.g. AIFF, WAV, FLAC, OGG, MP2, MP3, AAC, AMR, WMA) and within the size/duration limits before uploading
5. After a successful upload, poll or fetch the track resource to confirm transcoding has completed, since playback uses server-side transcoded output, not the raw uploaded bytes
6. To update metadata after upload, send a `PUT` to the track resource endpoint with the changed attributes — the audio asset itself cannot be replaced this way