[唤醒应答与快速端点]：完成唤醒后我在播报和本地VAD端点优化，包含缓冲清理、配置项和测试覆盖

src/owner_voice_pet/protocols.py

@@ -28,6 +28,9 @@ class AudioTransport(Protocol):
     def play_pcm(self, segment: AudioSegment, interrupt: bool = False) -> PlaybackResult:
         ...
 
+    def flush_input(self) -> int:
+        ...
+
     def stop(self) -> None:
         ...