refine tool提示语为更简洁风格，补充last_buffer_char属性及非VERBOSE模式流式输出换行逻辑，新增工具流式分隔符单元测试

app/agent/tools/impl/send_voice_message.py

@@ -41,7 +41,7 @@ class SendVoiceMessageTool(MoviePilotTool):
         message = kwargs.get("message") or ""
         if len(message) > 40:
             message = message[:40] + "..."
-        return f"正在发送语音回复: {message}"
+        return f"发送语音回复: {message}"
 
     def _supports_real_voice_reply(self) -> bool:
         channel = self._channel or ""