feat(zonos): OpenAI-ish REST adapter for asset-engine routing

Upstream Zonos ships only Gradio + Python SDK — no REST surface — so
asset-engine (which routes a clean JSON POST to /v1/audio/speech) can't
target it directly. Add a thin FastAPI adapter (stacks/zonos/adapter/):
POST /v1/audio/speech in front of the Zonos SDK, built FROM local/zonos
to reuse torch/CUDA/SDK. Returns a JSON envelope {audio, audio_format,
seed} — the seed rides back so asset-engine regenerate/fork can pin it
(Zonos is the fleet's first genuinely seedable TTS). compose gains a
zonos-api service on 8201; .env.example gains the port + voices dir.

stacks/zonos/README.md

@@ -13,7 +13,7 @@ Models ([`Zonos.from_pretrained()`](https://github.com/Zyphra/Zonos)):
 | hybrid | [Zyphra/Zonos-v0.1-hybrid](https://huggingface.co/Zyphra/Zonos-v0.1-hybrid) | Mamba-SSM; needs Ampere+ GPU + extra build deps |
 
 **Server:** irv-ml1 (Irvine, WireGuard-only)
-**Port:** 8199 (container Gradio listens on 7860)
+**Ports:** 8199 Gradio eval UI (container 7860) · 8201 REST adapter (container 8000)
 **GPUs:** pins to device 0 (RTX 3090) by default; ~6 GB VRAM
 **Image:** `local/zonos:v1` — built locally from a pinned git SHA of the
 upstream repo via docker buildx's git URL context
@@ -29,17 +29,37 @@ natural-language paralinguistic tags. Worth A/B-ing by ear against
 Chatterbox-Turbo (the research that prompted this stack explicitly said
 "benchmark Zonos against Chatterbox before choosing").
 
-## ⚠️ Audition surface, not skaldsong-pluggable (yet)
+## Two surfaces: Gradio eval (8199) + REST adapter (8201)
 
-The official repo ships a **Gradio WebUI + Python SDK only** — there is
-**no OpenAI-compatible `/v1/audio/speech` endpoint**. So this stack is
-for *auditioning quality*, not for wiring into skaldsong's engine
-router as-is. To promote Zonos to a real engine slot we'd need either:
+The official repo ships a **Gradio WebUI + Python SDK only** — no REST
+endpoint. So this stack runs two services:
 
-- the community FastAPI fork ([Zyphra/Zonos PR #73](https://github.com/Zyphra/Zonos/pull/73), adds REST + basic streaming), or
-- a thin OpenAI-compat adapter in front of the Python SDK.
+- **`zonos`** (8199) — upstream Gradio UI, for *auditioning quality by ear*.
+- **`zonos-api`** (8201) — a thin OpenAI-ish adapter we built
+  (`adapter/server.py`) exposing `POST /v1/audio/speech` so **asset-engine**
+  can route to Zonos like every other TTS in the catalog. Returns a JSON
+  envelope `{audio: <base64>, audio_format, seed}` — the `seed` rides back
+  so regenerate/fork can pin it (Zonos is the fleet's first seedable TTS).
 
-Both are a follow-up if Zonos earns a slot in the ear test.
+The adapter is built `FROM local/zonos:<tag>` (reuses torch/CUDA/SDK) and
+loads its own copy of the model (~6 GB on top of the Gradio service). Once
+Zonos earns a permanent slot, drop the Gradio service and keep the adapter.
+
+The community FastAPI fork ([PR #73](https://github.com/Zyphra/Zonos/pull/73))
+was the alternative; we chose the self-owned adapter over pinning to an
+unmerged fork.
+
+### Adapter request (example)
+
+```bash
+curl -sS http://10.100.79.3:8201/v1/audio/speech \
+  -H 'content-type: application/json' \
+  -d '{"input":"Hello from Zonos.","language":"en-us","seed":420}' \
+  | python3 -c 'import sys,json,base64; d=json.load(sys.stdin); open("out.wav","wb").write(base64.b64decode(d["audio"])); print("seed",d["seed"])'
+```
+
+Cloning: drop a 10–30s WAV in `/worktank/zonos/voices/` and pass its
+filename as `"voice"`. `GET /v1/audio/voices` lists what's available.
 
 ## Deploy