fix: 修复启动时清空数据库逻辑，适配新表结构

monitor.py

@@ -830,7 +830,9 @@ class MessageMonitor:
         if clear_db and self._msg_history:
             try:
                 conn = self._msg_history._get_conn()
-                conn.execute("DELETE FROM message_history")
+                conn.execute("DELETE FROM user_messages")
+                conn.execute("DELETE FROM bot_messages")
+                conn.execute("DELETE FROM ocr_staging")
                 conn.execute("DELETE FROM keyword_scores")
                 conn.commit()
                 conn.close()