fix: 修复批量导入义工号/工作组丢失 + 新增批量删除

- 批量解析：移除义工号强制纯数字校验（原 volunteerLooksLikeNo 逻辑错误导致 VOL-003、2024-A 等全部置空）；改为列数驱动：3列时智能探测是否工作组命中，4+列保留义工号原值、剩余段统一合并为工作组解析
- 后端 batch：user_groups 插入语句改为事务内按用户编译；义工号判断改为 null/undefined 严格检查，避免真值判断丢弃空字符串或 0 开头的值
- 新增 DELETE /users/batch：事务性批量删除部员（含 user_groups/hours 级联），返回实际删除 count
- 前端列表新增复选框列（表头 indeterminate 半选态），选中 1+ 条后工具栏显示「删除选中（N）」红色按钮，确认弹窗二次校验

server/src/routes/users.ts

@@ -187,13 +187,14 @@ router.post('/batch', authMiddleware, (req: AuthRequest, res: Response) => {
   try {
     db.execCompat('BEGIN');
     const insertUser = db.prepareCompat('INSERT INTO users (class, name, volunteer_no, group_id) VALUES (?,?,?,?)');
-    const insertUG = db.prepareCompat('INSERT OR IGNORE INTO user_groups (user_id, group_id) VALUES (?,?)');
 
     for (let i = 0; i < items.length; i++) {
       const raw = items[i] || {};
       const cls = String(raw.class || '').trim();
       const name = String(raw.name || '').trim();
-      const volunteer_no = raw.volunteer_no ? String(raw.volunteer_no).trim() || null : null;
+      const volunteer_no = (raw.volunteer_no === undefined || raw.volunteer_no === null)
+        ? null
+        : (String(raw.volunteer_no).trim() || null);
       if (!cls || !name) {
         failed++;
         results.push({ idx: i, ok: false, error: '班级和姓名不能为空', item: raw });
@@ -213,7 +214,10 @@ router.post('/batch', authMiddleware, (req: AuthRequest, res: Response) => {
       try {
         const info = insertUser.run(cls, name, volunteer_no, firstGroup);
         const userId = Number(info.lastInsertRowid);
-        for (const gid of groups) insertUG.run(userId, gid);
+        if (groups.length > 0) {
+          const insertUG = db.prepareCompat('INSERT OR IGNORE INTO user_groups (user_id, group_id) VALUES (?,?)');
+          for (const gid of groups) insertUG.run(userId, gid);
+        }
         success++;
         results.push({ idx: i, ok: true, id: userId, item: raw });
       } catch (e: any) {
@@ -232,4 +236,35 @@ router.post('/batch', authMiddleware, (req: AuthRequest, res: Response) => {
   }
 });
 
+router.delete('/batch', authMiddleware, (req: AuthRequest, res: Response) => {
+  const { ids } = req.body || {};
+  if (!Array.isArray(ids) || ids.length === 0) {
+    return res.status(400).json({ error: '请选择要删除的部员' });
+  }
+  const db = getDb();
+  const list: number[] = [];
+  for (const id of ids) {
+    const n = Number(id);
+    if (!isNaN(n) && n > 0 && !list.includes(n)) list.push(n);
+  }
+  if (list.length === 0) {
+    return res.status(400).json({ error: '请选择有效的部员' });
+  }
+  try {
+    db.execCompat('BEGIN');
+    const del = db.prepareCompat('DELETE FROM users WHERE id = ?');
+    let count = 0;
+    for (const id of list) {
+      const r = del.run(id);
+      count += (r?.changes ?? 0);
+    }
+    db.execCompat('COMMIT');
+    db.save();
+    res.json({ ok: true, deleted: count, total: list.length });
+  } catch (e: any) {
+    try { db.execCompat('ROLLBACK'); } catch {}
+    res.status(500).json({ error: e?.message || '批量删除失败' });
+  }
+});
+
 export default router;