v0.1.6

## 🎉 ACE-Step 1.5 XL (4B DiT) Release

We introduce the **XL series** — a larger 4B-parameter DiT decoder for higher audio quality. XL achieves **best scores across all 11 benchmark metrics**, surpassing all commercial and open-source models.

### New Models

| Model | Steps | CFG | HuggingFace |
|-------|:-----:|:---:|-------------|
| `acestep-v15-xl-base` | 50 | ✅ | [Link](https://huggingface.co/ACE-Step/acestep-v15-xl-base) |
| `acestep-v15-xl-sft` | 50 | ✅ | [Link](https://huggingface.co/ACE-Step/acestep-v15-xl-sft) |
| `acestep-v15-xl-turbo` | 8 | ❌ | [Link](https://huggingface.co/ACE-Step/acestep-v15-xl-turbo) |

- **Weights**: ~9GB (bf16) vs ~4.7GB for 2B
- **Min VRAM**: 12GB with offload, 20GB+ recommended
- **LM compatibility**: All LM models (0.6B/1.7B/4B) fully compatible

### Features
- Model download registry and VRAM management for XL (#989, #990)
- XL model code directories: xl_base, xl_sft, xl_turbo (#1001)
- MLX Apple Silicon support for XL (#1002)
- VRAM preflight check uses actual model size (#1003)
- UI VRAM warning for XL models (#1004)
- Documentation in 4 languages: en/zh/ja/ko (#1005)
- Training & LoRA support for XL (#1006)
- Deduplicated model config files (#1000)
- Default Gradio model changed to xl-turbo (#1009)
- Persist user preferences across sessions via localStorage (#1013)

### Bug Fixes
- Fix config_path lookup in VRAM guards and API /models endpoint (#1003)
- Fix MLX condition_embedder dimension mismatch for XL (#1002)
- Fix API auto-calculation for metadata params (duration/bpm) (#1023)
- Fix user preference restore regressions (#1025, #1026)
- Fix GenerationParams crash when None passed for numeric fields (#1027)
- Fix AAC/M4A source audio "invalid source audio" error in remix/extract (#1028)
- Fix empty values in restore_preferences causing Gradio crash on load (#1030)
- Fix cover/repaint using caller-supplied duration instead of src_audio duration (#1031, #1033)
- Fix cover/repaint/extract missing error when source audio not provided (#1035)
- Fix cover/repaint tasks with audio codes but no src_audio (#1036)

**Full Changelog**: https://github.com/ace-step/ACE-Step-1.5/compare/v0.1.5...v0.1.6