feat(message_summary): add group overview stats section

utils/wechat/message_to_db.py

@@ -551,6 +551,27 @@ class MessageStorage:
             logger.error(f"统计消息数量出错: {e}")
             return 0
 
+    def get_message_stats_by_date_range(self, group_id, start_time: datetime, end_time: datetime) -> Dict:
+        """获取指定时间范围内的群消息概览统计"""
+        try:
+            stats = self.message_db.get_message_stats_by_date_range(group_id, start_time, end_time)
+            logger.info(
+                f"群 {group_id} 在 {start_time} 至 {end_time} 的消息概览: "
+                f"total={stats.get('total_count', 0)}, participants={stats.get('participant_count', 0)}"
+            )
+            return stats
+        except Exception as e:
+            logger.error(f"获取消息概览统计出错: {e}")
+            return {
+                "total_count": 0,
+                "participant_count": 0,
+                "text_count": 0,
+                "image_count": 0,
+                "video_count": 0,
+                "link_count": 0,
+                "emoji_count": 0,
+            }
+
     def _format_messages_optimized(self, messages: list, all_contacts: dict) -> str:
         """优化的消息格式化方法，减少冗余