feat(transcriber): 添加 MLX Whisper 转录器支持

- 新增 MLXWhisperTranscriber 类，支持在 Apple 平台上进行转录。
- 更新 transcriber_provider.py，动态导入 MLX Whisper 转录器并添加相应的环境变量检查。
- 修改 .env.example 文件，更新 TRANSCRIBER_TYPE 配置说明以包含 mlx-whisper 选项。

backend/app/transcriber/transcriber_provider.py

@@ -1,4 +1,5 @@
 import os
+import platform
 
 from app.transcriber.whisper import WhisperTranscriber
 from app.transcriber.bcut import BcutTranscriber
@@ -6,13 +7,26 @@ from app.transcriber.kuaishou import KuaishouTranscriber
 from app.utils.logger import get_logger
 logger = get_logger(__name__)
 
+# 只在Apple平台且设置了环境变量时才导入MLX Whisper
+if platform.system() == "Darwin" and os.environ.get("TRANSCRIBER_TYPE") == "mlx-whisper":
+    try:
+        from app.transcriber.mlx_whisper_transcriber import MLXWhisperTranscriber
+        MLX_WHISPER_AVAILABLE = True
+        logger.info("MLX Whisper 可用，已导入")
+    except ImportError:
+        MLX_WHISPER_AVAILABLE = False
+        logger.warning("MLX Whisper 导入失败，可能未安装或平台不支持")
+else:
+    MLX_WHISPER_AVAILABLE = False
+
 logger.info('初始化转录服务提供器')
 
 # 维护各种转录器的单例实例
 _transcribers = {
     'whisper': None,
     'bcut': None,
-    'kuaishou': None
+    'kuaishou': None,
+    'mlx-whisper': None
 }
 
 def get_whisper_transcriber(model_size="base", device="cuda"):
@@ -51,13 +65,29 @@ def get_kuaishou_transcriber():
             raise
     return _transcribers['kuaishou']
 
+def get_mlx_whisper_transcriber(model_size="base"):
+    """获取 MLX Whisper 转录器实例"""
+    if not MLX_WHISPER_AVAILABLE:
+        logger.warning("MLX Whisper 不可用，请确保在Apple平台且已安装mlx_whisper")
+        raise ImportError("MLX Whisper 不可用，请确保在Apple平台且已安装mlx_whisper")
+        
+    if _transcribers['mlx-whisper'] is None:
+        logger.info(f'创建 MLX Whisper 转录器实例，参数：{model_size}')
+        try:
+            _transcribers['mlx-whisper'] = MLXWhisperTranscriber(model_size=model_size)
+            logger.info('MLX Whisper 转录器创建成功')
+        except Exception as e:
+            logger.error(f"MLX Whisper 转录器创建失败: {e}")
+            raise
+    return _transcribers['mlx-whisper']
+
 def get_transcriber(transcriber_type="fast-whisper", model_size="base", device="cuda"):
     """
     获取指定类型的转录器实例
     
     参数:
-        transcriber_type: 转录器类型，支持 "fast-whisper", "bcut", "kuaishou"
-        model_size: 模型大小，whisper 特有参数
+        transcriber_type: 转录器类型，支持 "fast-whisper", "bcut", "kuaishou", "mlx-whisper"(仅Apple平台)
+        model_size: 模型大小，whisper 和 mlx-whisper 特有参数
         device: 设备类型，whisper 特有参数
     
     返回:
@@ -67,6 +97,12 @@ def get_transcriber(transcriber_type="fast-whisper", model_size="base", device="
     if transcriber_type == "fast-whisper":
         whisper_model_size = os.environ.get("WHISPER_MODEL_SIZE",model_size)
         return get_whisper_transcriber(whisper_model_size, device=device)
+    elif transcriber_type == "mlx-whisper":
+        if not MLX_WHISPER_AVAILABLE:
+            logger.warning("MLX Whisper 不可用，回退到 fast-whisper")
+            whisper_model_size = os.environ.get("WHISPER_MODEL_SIZE",model_size)
+            return get_whisper_transcriber(whisper_model_size, device=device)
+        return get_mlx_whisper_transcriber(whisper_model_size)
     elif transcriber_type == "bcut":
         return get_bcut_transcriber()
     elif transcriber_type == "kuaishou":