fish-s2: docs + verify reflect actual API (POST /v1/tts, not OpenAI-compat)

After getting fish-s2 finally healthy on attempt #5, the playbook's
verify still failed because /v1/audio/voices doesn't exist. Discovery:
the Fish wrapper has a custom API surface, not OpenAI-compatible.
Real endpoints:

  POST /v1/tts             — synthesis (text body, optional `references`
                             field for voice cloning, returns audio/wav)
  GET  /v1/health          — liveness (used by Docker healthcheck)
  GET  /heartbeat          — alternate liveness signal
  GET  /                   — Swagger Editor UI for the OpenAPI spec

No /v1/audio/speech, /v1/audio/voices, /v1/models — those return 404.

Updated:
* Playbook verify — replaced the JSON-shape /v1/audio/voices check
  with a POST /v1/tts smoke that asserts a real RIFF WAV comes back.
* README API section — replaced the OpenAI-compat examples with
  Fish's actual {"text":"...","references":[...]} body shape.
* README disk footprint — corrected ~9 GB → ~11 GB (codec.pth was
  larger than I estimated; 1.9 GB + 9 GB safetensors).
* README Lessons learned section — recorded the 5-iteration deploy
  story so the next time we touch a Fish-style upstream we don't
  re-walk the dockerfile / target / pre-pull / API-shape traps.

playbooks/deploy-fish-s2.yaml

@@ -103,10 +103,20 @@ verify:
     shell: curl -sf -o /dev/null http://localhost:{{ host_port }}/v1/health
     changed_when: "false"
 
-  - name: /v1/audio/voices returns valid JSON
+  - name: /v1/tts returns a real WAV (POST with text body)
+    # Fish's API is NOT OpenAI-compatible — there's no /v1/audio/speech
+    # and no /v1/audio/voices. The single TTS endpoint is POST /v1/tts
+    # with at minimum {"text":"..."} returning audio/wav. Voice cloning
+    # is via reference= field in the body (paths under /app/references).
+    # Verify by POST + asserting the response is a real RIFF WAV.
     shell: |
-      curl -sf http://localhost:{{ host_port }}/v1/audio/voices \
-        | python3 -c "import json,sys; json.load(sys.stdin)"
+      out=$(mktemp --suffix=.wav)
+      curl -sf -X POST http://localhost:{{ host_port }}/v1/tts \
+        -H 'Content-Type: application/json' \
+        -d '{"text":"Verify."}' \
+        -o "$out" --max-time 30
+      file -b "$out" | grep -q '^RIFF.*WAVE'
+      rm -f "$out"
     changed_when: "false"
 
   - name: Container is running