Clarify temporary recording retention

Archive opted-in recordings in private bucket

Automatically fit sampled bass register with GM fallback

Fix bass sampler range and cover audible notes

Run YuE2 by default and fix sampler result accounting

Add sampled guitar and bass with effects; make YuE2 opt-in

Stream previews and remove duplicate initial drum beat

Generate melody and drum variants together

Prepare public Hum Space

Build Hum recording and generation Space