fix: 部员详情参与活动数据没对齐和补录时间显示问题

- 详情 activities 排序改为按登记时间倒序，新增 reg_at 字段
- formatDateRange 同一天合并显示，字符数减半避免被截断
- DataTable 给活动名/时间/时长列显式宽度，时间列加 pl-3 留白防切

server/src/routes/users.ts

@@ -76,11 +76,11 @@ router.get('/:id', (req: Request, res: Response) => {
   if (!raw) return res.status(404).json({ error: '部员不存在' });
   const user = enrichUser(raw);
   const activities = db.prepareCompat(`
-    SELECT a.id, a.title, a.start_time, a.end_time, h.hours, h.remark
+    SELECT a.id, a.title, a.start_time, a.end_time, h.hours, h.remark, h.created_at AS reg_at
     FROM hours h
     JOIN activities a ON h.activity_id = a.id
     WHERE h.user_id = ?
-    ORDER BY a.start_time DESC
+    ORDER BY h.created_at DESC, a.start_time DESC
   `).all(id);
   res.json({ ...user, activities });
 });