Use latest user message time for thread timestamps - #1996

Bugbot Analysis Progress (5m 58s elapsed)

✅ Gathered PR context (3s)
✅ Completed bug detection (5m 54s)
✅ Posted analysis results (1s)

Final Result: Bugbot completed review - no issues found. 1 previously reported issue remain unresolved.

Request ID: serverGenReqId_fb08ba13-693a-4817-8ee5-aaf05651e6c6