fish-cpp: switch to resident s2 server + proxy shim — fix per-request CUDA init dominating wall time

Subprocess-per-request architecture forced CUDA + model load on every
/v1/tts call (~10-20s init, then 5-15s generation). Even though CUDA
is now actually being used (`-c 0` fix landed), 32s for "Verify."
proved per-request init was the bottleneck.

s2.cpp ships a built-in HTTP server (`--server -H -P`) that keeps the
model resident on the GPU. Refactor:

* entrypoint.sh — backgrounds `s2 --server -P 3030 -c 0 -m ... -t ...`,
  waits for it to bind 3030, then foregrounds uvicorn. tini supervises
  via `wait -n` so either child dying takes down the container.

* server.py — drops subprocess.run; instead httpx-POSTs Fish-shaped
  /v1/tts JSON to s2's localhost:3030/generate (multipart form: text
  + optional prompt_text/prompt_audio for cloning). Model load + CUDA
  init now happen once at container start, not per-request.

* Dockerfile — added httpx (shim dep), curl (entrypoint readiness
  probe), and the entrypoint.sh COPY+chmod. CMD now invokes
  entrypoint.sh instead of uvicorn directly.

* deploy-fish-cpp.yaml — uploads entrypoint.sh alongside server.py.

playbooks/deploy-fish-cpp.yaml

@@ -66,6 +66,12 @@ steps:
       dest: "{{ compose_dir }}/server.py"
       mode: "0644"
 
+  - name: Upload entrypoint.sh (starts s2 server + uvicorn shim)
+    upload:
+      src: stacks/fish-cpp/entrypoint.sh
+      dest: "{{ compose_dir }}/entrypoint.sh"
+      mode: "0755"
+
   - name: Seed .env from template (only if absent)
     upload:
       src: stacks/fish-cpp/.env.example