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/compose.yaml

@@ -63,3 +63,40 @@ services:
       - homepage.icon=mdi-waveform
       - homepage.description=Expressive multilingual TTS + cloning, 44kHz (Gradio eval, irv-ml1)
       - homepage.href=http://10.100.79.3:${ZONOS_PORT}
+
+  # OpenAI-ish REST adapter (POST /v1/audio/speech) that asset-engine
+  # routes to — upstream Zonos has no REST surface, only Gradio + SDK.
+  # Built FROM the gradio image above (reuses torch/CUDA/SDK); loads its
+  # own copy of the model, so it adds ~6 GB VRAM on top of the gradio
+  # service. Drop the gradio service once Zonos earns a permanent slot.
+  zonos-api:
+    image: local/zonos-api:${ZONOS_TAG}
+    build:
+      context: ./adapter
+      dockerfile: Dockerfile
+      args:
+        ZONOS_BASE: local/zonos:${ZONOS_TAG}
+    container_name: zonos-api
+    restart: unless-stopped
+    runtime: nvidia
+    depends_on:
+      - zonos
+    ports:
+      - "${ZONOS_BIND:-0.0.0.0}:${ZONOS_API_PORT}:8000"
+    environment:
+      - NVIDIA_VISIBLE_DEVICES=${ZONOS_GPU_DEVICES:-0}
+      - NVIDIA_DRIVER_CAPABILITIES=compute,utility
+      - HF_HOME=/app/hf_cache
+      - ZONOS_MODEL=${ZONOS_MODEL:-Zyphra/Zonos-v0.1-transformer}
+      - ZONOS_VOICES_DIR=/app/voices
+    volumes:
+      - ${ZONOS_CACHE_DIR}:/app/hf_cache
+      # Reference clips for zero-shot cloning, selected by the `voice`
+      # request field (filename under this dir).
+      - ${ZONOS_VOICES_DIR}:/app/voices:ro
+    healthcheck:
+      test: ["CMD-SHELL", "python3 -c \"import urllib.request,sys; urllib.request.urlopen('http://127.0.0.1:8000/health', timeout=5); sys.exit(0)\""]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 600s