feat(conversation): TTS 投递与 WebSocket 管线；客户端播放门禁与会话页联动；COS 键与迁移脚本调整

api/app/features/conversation/history_store.py

@@ -85,9 +85,9 @@ class ConversationHistoryStore:
         audio_duration_seconds: int | None,
         tts_audio_urls: list[str] | None,
         segment_id: str | None,
-    ) -> None:
+    ) -> str | None:
         if not responses:
-            return
+            return None
         human_ts = user_message_timestamp or _utc_now()
         if human_ts.tzinfo is None:
             human_ts = human_ts.replace(tzinfo=timezone.utc)
@@ -122,6 +122,7 @@ class ConversationHistoryStore:
         await self._touch_conversation(conversation_id, occurred_at=ai_ts)
         await self._db.commit()
         await self._sync_redis_best_effort(conversation_id)
+        return ai.id
 
     async def attach_ai_tts_audio_urls(
         self,