fix: 豆包引擎补全pitch_ratio和volume_ratio参数

前端声调/音量滑块现在对豆包引擎也生效了

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/services/doubao_service.py

@@ -28,6 +28,8 @@ def synthesize_doubao(text, speed=1.0, pitch=0, volume=1.0, emotion='neutral'):
             'voice_type': 'S_LK0j18H72',
             'encoding': 'mp3',
             'speed_ratio': speed,
+            'pitch_ratio': max(0.1, min(3.0, 1.0 + pitch / 12)),  # 前端-12~12映射到0.1~3.0
+            'volume_ratio': max(0.1, min(3.0, volume)),            # 前端0~10，API 0.1~3.0
             'bitrate': 128000,
         },
         'request': {