feat(tts): migrate RP-surface TTS chatterbox-fast → dots-tts

Swap the voice synthesis backend from chatterbox-fast (:8197 bespoke /tts)
to dots-tts (rednote-hilab dots.tts-soar, :8198 OpenAI-shaped
/v1/audio/speech), operator-directed after an A/B win. tts.py stays the
single swap seam.

- gateway body OpenAI-shaped: {input, voice, response_format, stream}
  (was chatterbox {text, voice, format, stream})
- sample rate 24000 -> 48000 Hz (browser Web Audio SR)
- default voice glados_25s -> glados; donut voice carries over
- serialized single-consumer (satisfied by the existing DEC-5 lock)
- affect stays dropped (dots has no emotion knob, same as chatterbox)

DOTS_TTS_URL replaces CHATTERBOX_TTS_URL; RATATOSKR_TTS_URL override
unchanged. chatterbox-fast :8197 kept up as rollback. Contract amended
(donut_voiced_interview.contract.md). Live-verified end-to-end on :8765
(RIFF/WAVE 48kHz mono s16le through /api/tts). 520 tests green.

tests/test_tts.py

@@ -1,10 +1,10 @@
-"""Tests for ratatoskr.tts — the STREAMING chatterbox-fast gateway client.
+"""Tests for ratatoskr.tts — the STREAMING dots-tts gateway client.
 
 tts_stream proxies the gateway's chunked response verbatim (no buffering, no header
 rewrite — the placeholder-size streaming WAV is meant to be played progressively). It
-is the sole synthesis primitive: chatterbox chunks arbitrary-length text internally, so
-there is no client-side chunk-and-concatenate (retired with the Zonos migration), and no
-affect dials (Turbo has no emotion knob). The mid-stream degrade policy is folded in.
+is the sole synthesis primitive: dots streams a whole turn from one call, so there is
+no client-side chunk-and-concatenate, and no affect dials (dots has no emotion knob).
+The mid-stream degrade policy is folded in.
 """
 
 import httpx
@@ -12,13 +12,13 @@ import pytest
 import respx
 
 from ratatoskr.tts import (
-    CHATTERBOX_TTS_URL,
+    DOTS_TTS_URL,
     TtsUnavailable,
     gateway_body,
     tts_stream,
 )
 
-_URL = "http://tts.example/tts"
+_URL = "http://tts.example/v1/audio/speech"
 # The gateway's streaming WAV bytes (placeholder 0xFFFFFFFF sizes). We pass them through
 # untouched, so the content only has to round-trip.
 _WAV = (
@@ -50,34 +50,32 @@ class _RaisingByteStream(httpx.AsyncByteStream):
 
 
 class TestGatewayBody:
-    def test_bespoke_chatterbox_schema(self) -> None:
+    def test_openai_dots_schema(self) -> None:
         b = gateway_body("hi", "donut")
-        assert b["text"] == "hi"          # "text", not "input"
+        assert b["input"] == "hi"              # OpenAI "input", not chatterbox "text"
         assert b["voice"] == "donut"
-        assert b["format"] == "wav"       # DEC-3 — "format", not "response_format"
-        assert b["stream"] is True        # DEC-2 — play-as-it-arrives
+        assert b["response_format"] == "wav"   # DEC-3 — "response_format", not "format"
+        assert b["stream"] is True             # DEC-2 — play-as-it-arrives
 
     def test_default_sampling_no_client_side_curbs(self) -> None:
-        # DEC-9 (real cause): the long-turn garble was Turbo over-running its GENERATION TAIL,
-        # fixed SERVER-SIDE (:v2 max_chunk_chars=250). A client sampling curb was
-        # counterproductive (tight sampling pulls the garble onset earlier), so gateway_body
-        # sends NO temperature/top_p/top_k — the gateway's defaults govern.
+        # No client sampling curbs — the gateway's defaults govern (a client-side curb
+        # was counterproductive on the prior backend and dots exposes no such need).
         b = gateway_body("a long turn", "donut")
         for knob in ("temperature", "top_p", "top_k"):
             assert knob not in b
 
-    def test_no_zonos_era_fields(self) -> None:
-        # The Zonos body fields are gone: no OpenAI `input`/`response_format`, no
-        # `language` pin (DEC-9 retired), no affect dials (DEC-7 retired).
-        b = gateway_body("hi", "Cora")
-        for dead in ("input", "response_format", "language", "emotion_valence",
+    def test_no_chatterbox_or_zonos_era_fields(self) -> None:
+        # The chatterbox bespoke names + Zonos-era fields are gone: no `text`/`format`
+        # (chatterbox), no `language` pin, no affect dials (DEC-7 retired).
+        b = gateway_body("hi", "glados")
+        for dead in ("text", "format", "language", "emotion_valence",
                      "emotion_arousal", "emotion_enabled", "emotion_strength"):
             assert dead not in b
 
 
 class TestTtsStream:
     @respx.mock
-    async def test_streams_chunks_and_posts_bespoke_body(self) -> None:
+    async def test_streams_chunks_and_posts_openai_body(self) -> None:
         route = respx.post(_URL).mock(return_value=httpx.Response(200, content=_WAV))
         async with httpx.AsyncClient() as client:
             out = await _drain(tts_stream("hello there", voice="donut", client=client, url=_URL))
@@ -85,19 +83,19 @@ class TestTtsStream:
         import json as _json
 
         body = _json.loads(route.calls.last.request.content)
-        assert body["text"] == "hello there"
+        assert body["input"] == "hello there"
         assert body["voice"] == "donut"
-        assert body["format"] == "wav"
+        assert body["response_format"] == "wav"
         assert body["stream"] is True
 
     @respx.mock
-    async def test_default_url_is_chatterbox(self) -> None:
-        route = respx.post(CHATTERBOX_TTS_URL).mock(
+    async def test_default_url_is_dots(self) -> None:
+        route = respx.post(DOTS_TTS_URL).mock(
             return_value=httpx.Response(200, content=_WAV)
         )
         async with httpx.AsyncClient() as client:
             await _drain(tts_stream("hi", voice="donut", client=client))
-        assert route.called  # the module default points at the chatterbox gateway
+        assert route.called  # the module default points at the dots-tts gateway
 
     @respx.mock
     async def test_non_200_open_raises_before_any_chunk(self) -> None: