test(post): rewrite separate_stems test for demucs.apply.apply_model path

feat(deploy): preload all hub models + warm demucs on spaces

fix(deploy): per-mode duration estimator handles cover/extend/edit/lyrics signatures

feat(post): add demucs stems, lufs normalisation, mp3 export

feat(lyrics): add qwen 2.5 7b lazy loader with mlx and transformers backends

feat(pipeline): wire cover/extend/edit task_types in studio.generate

feat(modes): add cover, extend, edit handlers with sub-mode dispatch

fix(lora): point manifest at the actually-published ACE-Step LoRAs

feat(backend): apply lora stack before mode dispatch

feat(lora): add single-lora stack apply + disable

feat(lora): add preset registry with hf-download helper

feat(lora): add safetensors header sniff with ace-step module check

refactor(pipeline): rewrite for real acestep AceStepHandler+LLMHandler api

fix(pipeline): correct hf model id to acestep-v15-xl-sft

test(smoke): add gpu smoke for minimum generate path

feat(backend): add ace-step studio backend with dispatch + zerogpu wrap

feat(modes): add generate mode handler with input validation

feat(pipeline): lazy ace-step singleton with device-aware load

chore(fmt): apply ruff format and remove unused import in conftest

feat(ui): add brutalist mono theme tokens and responsive css

feat(pipeline): add device autodetect with mps-safe vram limit

test: add pytest scaffolding