feat: add bit_rate parameter to AudioSpeechRequest (ENG-84936)

Add bit_rate as an optional integer enum to the TTS request schema.
Only applicable with response_format=mp3. Valid values: 32000, 64000,
96000, 128000 (default), 192000.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rishabh-bhargava

openapi.yaml

@@ -9835,6 +9835,16 @@ components:
           type: integer
           default: 44100
           description: Sampling rate to use for the output audio. The default sampling rate for canopylabs/orpheus-3b-0.1-ft and hexgrad/Kokoro-82M is 24000 and for cartesia/sonic is 44100.
+        bit_rate:
+          type: integer
+          description: Bitrate of the MP3 audio output in bits per second. Only applicable when response_format is mp3. Higher values produce better audio quality at larger file sizes. Default is 128000. Currently supported on Cartesia models.
+          default: 128000
+          enum:
+            - 32000
+            - 64000
+            - 96000
+            - 128000
+            - 192000
         stream:
           type: boolean
           default: false