feat: 新增腾讯云ASR服务，支持按配置切换ASR提供商

- 新增tencent_asr_service.py腾讯云一句话识别
- 优化asr_service.py
- 更新services/__init__.py按ASR_PROVIDER切换whisper/tencent
- 更新requirements.txt

Co-authored-by: Cursor <cursoragent@cursor.com>

api/services/__init__.py

@@ -1,7 +1,28 @@
 """
 服务模块
+通过环境变量 ASR_PROVIDER 选择 ASR 实现：
+  - ASR_PROVIDER: whisper（默认，本地 faster-whisper）| tencent（腾讯云一句话识别）
 """
-from .asr_service import asr_service
+import os
+import logging
+
+logger = logging.getLogger(__name__)
+
+# =============================================================================
+# ASR Provider 选择
+# =============================================================================
+ASR_PROVIDER = os.getenv("ASR_PROVIDER", "whisper").lower()
+
+if ASR_PROVIDER == "tencent":
+    from .tencent_asr_service import tencent_asr_service as asr_service
+    logger.info("ASR Provider: 腾讯云一句话识别")
+else:
+    from .asr_service import asr_service
+    logger.info("ASR Provider: faster-whisper（本地）")
+
+# =============================================================================
+# TTS 及其他服务
+# =============================================================================
 from .tts_service import tts_service
 from .llm_service import llm_service
 from .redis_service import redis_service
@@ -12,4 +33,3 @@ __all__ = [
     "llm_service",
     "redis_service",
 ]
-