feat(portal-shell): extract domain API layer and migrate 31 widgets

Task 4-10 of portal-shell data abstraction plan (M1-M2).

Add 7 domain API modules under src/lib/api/ (parent/admin/teacher/
student/universal/sidebar/topbar), each exposing semantic hooks that
wrap useWidgetQuery/useWidgetMutation and return flattened domain
models. Widget code now imports from @/lib/api instead of inlining
gql literals.

- 31 widgets migrated (gql literal count in widgets: 0)
- 7 test files (85 cases, all passing)
- topbar.useNotifications renamed to useNotificationBell to avoid
  barrel export collision with universal.useNotifications
- typecheck + lint (0 errors) + test (85/85) verified

apps/portal-shell/src/widgets/topbar/user-menu/index.tsx

@@ -3,42 +3,22 @@
 /**
  * user-menu（topbar / top）
  *
- * 通过 useWidgetQuery 查询 apollo-router → iam 子图的 me 数据。
+ * 通过 useCurrentUser 查询 apollo-router → iam 子图的 me 数据。
  * 展示用户头像 + 下拉菜单（昵称 / 邮箱 / 角色）。
  *
  * 关联：portal-shell spec §5.6 统一 Hook、M8 验收
  */
-import { gql } from "@apollo/client";
 import { useState } from "react";
-import { useWidgetQuery } from "@/lib/useWidgetQuery";
+import { useCurrentUser } from "@/lib/api/topbar";
 import { useAuth } from "@/providers/AuthProvider";
 import type { PluginProps } from "@/lib/types";
 
-const GET_CURRENT_USER = gql`
-  query GetCurrentUser {
-    me {
-      id
-      name
-      email
-      role
-    }
-  }
-`;
-
-interface MeQueryData {
-  me: { id: string; name: string; email: string; role: string } | null;
-}
-
 export default function UserMenu(_props: PluginProps): React.ReactElement {
   const { user } = useAuth();
   const [open, setOpen] = useState(false);
 
-  const { data } = useWidgetQuery<MeQueryData, Record<string, never>>(
-    GET_CURRENT_USER,
-    {},
-  );
+  const { data: me } = useCurrentUser();
 
-  const me = data?.me;
   const displayName = me?.name ?? user.name;
   const displayEmail = me?.email ?? user.email;
   const displayRole = me?.role ?? user.role;