PreviewChatMessage 类型:新增 status(loading/done/error)、error、audioBlob 字段DialogueAPI 接口:createSession / speak / getReport 方法TranscriptEvent / TokenEvent / DoneEventRealDialogueAPI:fetch + ReadableStream,对接后端 3 个接口MockDialogueAPI:模拟 transcript + 逐 token 输出messages refsendStudentMessage(audioBlob):添加学生消息 → 调 speak → 流式消费 → 完成/失败expires_at 显示倒计时