feat(export): 新增活动时长总表（矩阵）+ 移除Logo

- 后端 POST /api/export 新增 include_activity_matrix：部员×活动矩阵行，列=所有活动（start_time DESC排），_total尾列
- 前端 Export 新增 06 卡片「活动时长总表（矩阵）」：部员+义工号 左固定列，活动列160px宽表头显示日期副标题，值>0高亮主色+浅底，总时长bg-primary-50
- Excel 新增「活动时长总表(矩阵)」Sheet：列名=活动标题，末列总时长
- 移除Brand组件所有img Logo渲染，纯标题，减小侧栏移动端头部视觉噪音
- 前后端 tsc --noEmit exit 0 + vite build exit 0；浏览器 E2E 验证矩阵张三/校园志愿宣传活动=2.00/总时长 2.00 h

server/src/routes/export.ts

@@ -5,7 +5,7 @@ import { authMiddleware, AuthRequest } from '../middleware/auth';
 const router = Router();
 
 router.post('/', authMiddleware, (req: AuthRequest, res) => {
-  const { include_users, include_activities, include_hours, include_user_totals, include_user_activities } = req.body || {};
+  const { include_users, include_activities, include_hours, include_user_totals, include_user_activities, include_activity_matrix } = req.body || {};
   const db = getDb();
   const result: any = {};
 
@@ -65,6 +65,37 @@ router.post('/', authMiddleware, (req: AuthRequest, res) => {
       return { ...u, activities: acts };
     });
   }
+  if (include_activity_matrix) {
+    const activities = db.prepareCompat(`
+      SELECT id, title, start_time FROM activities ORDER BY start_time DESC, id DESC
+    `).all() as any[];
+    const users = db.prepareCompat(`
+      SELECT u.id, u.class, u.name, u.volunteer_no, g.name AS group_name
+      FROM users u LEFT JOIN work_groups g ON u.group_id = g.id
+      ORDER BY u.class, u.name
+    `).all() as any[];
+    const hoursRows = db.prepareCompat(`
+      SELECT user_id, activity_id, hours FROM hours
+    `).all() as any[];
+    const matrix: Record<string, number> = {};
+    for (const r of hoursRows) {
+      const key = `${r.user_id}|${r.activity_id}`;
+      matrix[key] = (matrix[key] || 0) + Number(r.hours || 0);
+    }
+    result.activity_matrix = {
+      activities,
+      users: users.map((u) => {
+        const row: Record<string, any> = { id: u.id, class: u.class, name: u.name, volunteer_no: u.volunteer_no, group_name: u.group_name };
+        for (const a of activities) {
+          row[String(a.id)] = Number((matrix[`${u.id}|${a.id}`] || 0).toFixed(2));
+        }
+        row._total = Number(
+          activities.reduce((s: number, a: any) => s + (Number(row[String(a.id)]) || 0), 0).toFixed(2)
+        );
+        return row;
+      }),
+    };
+  }
   res.json(result);
 });