fix: 修复cleaned_item未定义错误 - 调整清理顺序

问题：QQ轮询时cleaned_item变量未定义
根因：OCR清理函数调用顺序错误，在使用变量后才定义变量
修复：将cleaned_item = self._clean_ocr_prefix(item)移到使用前

monitor.py

@@ -5269,12 +5269,12 @@ class MessageMonitor:
                 self._last_screenshot_hash.pop(platform, None)
                 self._last_new_msg_time[platform] = time.time()
             else:
+                # ⭐ 清理OCR噪声前缀（如"必选，"）后再搜索知识库
+                cleaned_item = self._clean_ocr_prefix(item)
                 self._last_new_msg_time[platform] = time.time()
                 self._last_msg[platform] = cleaned_item
                 engine_tag = self._last_chosen_engine.get(platform, "")
                 logger.info(f"[{platform}] 新消息[{engine_tag}]: {item[:60]}")
-                # ⭐ 清理OCR噪声前缀（如"必选，"）后再搜索知识库
-                cleaned_item = self._clean_ocr_prefix(item)
                 # ⚠️ 急停检查：回复前最后检查，防止急停后仍然发送
                 if not self._running:
                     return