AbstractMusic v0.1.12

Changed

• Collapsed the public ACE-Step surface to a single acestep backend backed by the package-owned
  AceStepPipeline adapter and removed the old acestep-v15 / acestep-diffusers backend split.
• Removed vendored ACE-Step v1.5 model/runtime code from the package and kept local ACE-Step
  execution on Hugging Face weights plus AbstractMusic-owned orchestration only.
• Reduced the packaged ACE-Step discovery catalog to reviewed official checkpoints under the public
  acestep backend and stopped surfacing unreviewed community conversions in the default model
  registry.
• Made AbstractCore music discovery report backend-oriented provider ids and only return
  providers/models whose runtime is actually usable in the current environment.

Docs

• Updated README, getting-started, API, models, troubleshooting, backlog overview, and
  llms-full.txt for the single-backend ACE-Step contract and truthful discovery behavior.
• Repaired the AI-readable docs index link to ACKNOWLEDGMENTS.md.