feat(observability): Phase2.3 媒体/LLM 可观测面板(后端归因聚合+前端页) 并修复 token_usage_logs trace_id 写入(chat_service/im_llm) [v2026.07.19.5]

backend/python/app/api/chat_service.py

@@ -16,7 +16,7 @@ import httpx
 import os
 import logging
 from ..database import get_db, SessionLocal
-from app.core.observability import span
+from app.core.observability import span, get_trace_id
 from ..models import (
 
 
@@ -1743,6 +1743,8 @@ async def _send_message_core(
 
 
             conversation_id=conv_id,
+            trace_id=get_trace_id(),
+