fix: 批量添加工工作组调试回显 + 完整验证写入

- 后端 /users/batch 返回每条成功记录的 groups_written/groups_expected/group_ids_out；失败记录返回 group_ids_seen/count
- 前端 submitBatch：console.log 打印发送 payload 和响应；弹窗汇总工作组实际/期望写入数；任何异常的行都显示后端实际解析出的 group_ids_out，失败行同时显示后端收到的 group_ids_seen
- 本地模拟后端 sql.js 写入 user_groups 100% 正确（场景A/B测试均 changes=1，聚合查询正确），此提交部署后通过控制台和弹窗即可精确定位问题在哪一跳（前端发送 vs 后端解析 vs 数据库写入）
- npm run build 通过

server/src/routes/users.ts

@@ -214,17 +214,36 @@ router.post('/batch', authMiddleware, (req: AuthRequest, res: Response) => {
       try {
         const info = insertUser.run(cls, name, volunteer_no, firstGroup);
         const userId = Number(info.lastInsertRowid);
+        let ugCount = 0;
         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);
+          for (const gid of groups) {
+            const ugInfo = insertUG.run(userId, gid);
+            if ((ugInfo?.changes ?? 0) > 0) ugCount++;
+          }
         }
         success++;
-        results.push({ idx: i, ok: true, id: userId, item: raw });
+        results.push({
+          idx: i,
+          ok: true,
+          id: userId,
+          item: raw,
+          groups_written: ugCount,
+          groups_expected: groups.length,
+          group_ids_out: groups.slice(),
+        } as any);
       } catch (e: any) {
         failed++;
         let err = e?.message || '添加失败';
         if (String(err).includes('UNIQUE')) err = '该班级下已存在同名部员';
-        results.push({ idx: i, ok: false, error: err, item: raw });
+        results.push({
+          idx: i,
+          ok: false,
+          error: err,
+          item: raw,
+          group_ids_seen: Array.isArray(raw.group_ids) ? raw.group_ids : null,
+          group_ids_count: Array.isArray(raw.group_ids) ? raw.group_ids.length : 0,
+        } as any);
       }
     }
     db.execCompat('COMMIT');