docs(zonos-engine): capture the production ZONOS2 :1920 launch config (was live-only)

The Zonos TTS engine that zonos-gateway fronts (irv-ml1 3090, feeds asset-engine +
gateway-chat) ran as a bare native process with its real invocation existing ONLY
in the running process argv — the committed harness/zonos_server.sh on irv-ml1 was
STALE (said A6000/:1919, no perf flags; live is 3090/:1920 with cuda-graph/num-pages/
max-running-requests/memory-ratio). Captured the corrected canonical invocation +
tunables + the containerization plan here so the config survives a process death.

Engine = stock Zyphra/Zonos2 @ 194c0a3 (no custom PFI server code); torch 2.9.1+cu128;
15 GB HF weights. Next: containerize in-place on the 3090 (operator: keep off the
A6000, it OOMs under ComfyUI). Not yet built — this commit is the config capture only.

stacks/zonos-engine/.env.example

@@ -0,0 +1,23 @@
+# zonos-engine tunables — ZONOS2 native TTS engine (:1920, irv-ml1 3090).
+# Copy to .env on the host. These feed both zonos2-server.sh (native) and the
+# eventual container CMD/compose. Values captured from the live process 2026-07-16.
+
+# Upstream repo (github.com/Zyphra/Zonos2) commit to pin — reproducibility.
+ZONOS_COMMIT=194c0a3
+ZONOS_MODEL=Zyphra/ZONOS2
+
+# Endpoint
+ZONOS_PORT=1920
+
+# GPU — 3090 (irv-ml1 device 0). Operator 2026-07-16: keep OFF the A6000 (it OOMs
+# under ComfyUI load). Container: NVIDIA_VISIBLE_DEVICES=0; native: the 3090 UUID.
+ZONOS_ENGINE_GPU_ID=0
+
+# Serving/perf flags (paged KV + cuda graphs; tuned to co-exist on the packed 3090).
+ZONOS_CUDA_GRAPH_MAX_BS=1
+ZONOS_NUM_PAGES=16384
+ZONOS_MAX_RUNNING_REQUESTS=2
+ZONOS_MEMORY_RATIO=0.3
+
+# HF weights cache (~15 GB, models--Zyphra--ZONOS2) — MOUNT, do not bake into the image.
+HF_HOME=/home/lkraven/.cache/huggingface