ace-step + stable-audio-open: deploy music + SFX generation to irv-ml1

Two new audio-generation stacks alongside the TTS slate:

ace-step :8210 — Apache 2.0 music generation foundation model
(hybrid diffusion + LLM). Lyric-aware multi-minute songs. ~10-12 GB
VRAM during inference, A6000-pinned. Custom Dockerfile patches
upstream's torch/cu126 resolution bug (--extra-index-url cu126 was
falling back to pypi-default cu13 wheels, mismatching torchvision).

stable-audio-open :8211 — Stability AI 1.21B latent-diffusion SFX +
ambience. Up to 47s clips at 44.1 kHz. ~6 GB VRAM in fp16,
A6000-pinned. Custom FastAPI shim around diffusers' StableAudioPipeline
(no upstream HTTP server). Dockerfile pins torchsde explicitly —
diffusers doesn't pull it as a hard dep but
CosineDPMSolverMultistepScheduler needs it.

stacks/ace-step/README.md

@@ -0,0 +1,53 @@
+# ace-step
+
+ACE-Step 1.5 — Apache 2.0 open-source music generation foundation
+model. Hybrid diffusion + LLM. Generates lyric-aware multi-minute
+songs (vocals + instrumentation).
+
+| | |
+|---|---|
+| host | `irv-ml1` |
+| port | `8210` |
+| GPU | A6000 (`device_ids: ["1"]`) |
+| VRAM | ~10-12 GB during inference |
+| upstream | https://github.com/ace-step/ACE-Step |
+| license | Apache 2.0 |
+
+## API surface
+
+`infer-api.py` (FastAPI) exposes:
+
+- `GET /health` — liveness, returns 200 once the process is up
+  (model is lazy-loaded on first /generate).
+- `POST /generate` — body: `ACEStepInput` Pydantic model with
+  ~27 params (prompt, lyrics, audio_duration, guidance_scale, etc.).
+  Returns `{status, output_path, message}`.
+
+The container does NOT expose the Gradio UI — we override the upstream
+default `python3 acestep/gui.py` with `python3 infer-api.py`. If you
+want the Gradio UI for ad-hoc experimentation, run a one-off:
+
+```bash
+ssh irv-ml1 'docker exec -it ace-step python3 acestep/gui.py --server_name 0.0.0.0 --port 7865'
+```
+
+…and port-forward 7865 to your laptop.
+
+## Deploy
+
+```bash
+scripts/elway irv-ml1 --playbook playbooks/deploy-ace-step.yaml
+```
+
+Idempotent. Cold build is ~10-15 min (CUDA + torch + transformers +
+spacy + audio deps). First `/generate` triggers the model download
+(~5-10 GB) and warmup (~30-60 s).
+
+## Tunables
+
+See `.env.example` — copy to `.env` on the host (lives at
+`/opt/docker/compose/ace-step/.env`, gitignored). Common knobs:
+
+- `ACE_STEP_SHA` — pin upstream commit
+- `ACE_STEP_GPU_DEVICES` — GPU index
+- `ACE_STEP_*_DIR` — bind-mount paths under `/worktank/ace-step/`