Upload links

How create_upload_link lets a user transcribe their own song, and the tasks it accepts.

AI apps cannot pass audio files to tools, so uploads happen on groovesheet.net:

Call create_upload_link with a task. Give the user the returned url.
The user uploads there and gets a free preview. Only they can unlock the full song.
Call get_upload_status with the code until it is preview_ready or completed.

Links work once, belong to the account that made them and expire after 24 hours.

Tasks

`task`	Result
`drums`	Drum sheet music, MIDI and stem
`piano`	Piano sheet music and MIDI
`guitar`	Guitar sheet music with TAB, and MIDI
`bass`	Bass sheet music and MIDI
`chords`	Chord chart from the full mix
`stems`	Every part as separate audio
`drums_midi`	Drum MIDI only
`piano_midi`	Piano MIDI only