feat(web): add role-aware React dashboards

Add student and teacher dashboard variants backed by existing APIs, retain the administrative overview for management roles, and provide responsive navigation back to legacy routes that have not migrated yet.

web-react/MIGRATION_MATRIX.md

@@ -5,7 +5,7 @@
 | 路由 | 页面 | 角色/公开范围 | 关键合同 | 状态 |
 | --- | --- | --- | --- | --- |
 | `/login` | 登录 | 公开 | 验证码、密码、TOTP、SSO 设置、会话落盘 | building |
-| `/dashboard` | 教务总览 | 已登录用户 | `GET /api/dashboard`、角色视图、待办和学期 | building |
+| `/dashboard` | 角色化首页 | 已登录用户 | 管理总览；学生课表/消息/考试/预警；教师教学班/成绩登记进度 | verification |
 | `/account` | 个人账户 | 已登录用户 | TOTP、恢复码、SSO 绑定；Passkey 浏览器仪式尚未开放 | verification |
 | `/users` | 用户与权限 | SuperAdmin | 列表、筛选、分页、创建、启停、重置密码、角色范围、Excel | verification |