README: Apple MPS fork focus; use HeartCodec 20260123

- README: Position as Apple Silicon/MPS fork, remove CUDA/Windows/Docker
  focus, remove trademarked references, use audiohacking repo URLs
- music_service: HF_HEARTCODEC_REPO -> HeartCodec-oss-20260123 (recommended)

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: qxip