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/global-search/index.tsx

@@ -0,0 +1,78 @@
+"use client";
+
+/**
+ * global-search（topbar / top）
+ *
+ * 通过 useGlobalSearch 查询 apollo-router 的 search 数据。
+ * 输入关键词后显示搜索建议下拉，点击结果导航到对应页面。
+ *
+ * 关联：portal-shell spec §5.6 统一 Hook、M8 验收
+ */
+import { useState } from "react";
+import { useRouter } from "next/navigation";
+import { useGlobalSearch, type SearchResult } from "@/lib/api/topbar";
+import type { PluginProps } from "@/lib/types";
+
+const TYPE_PATH_MAP: Record<string, string> = {
+  student: "/students",
+  class: "/classes",
+  exam: "/exams",
+  homework: "/homework",
+  announcement: "/announcements",
+};
+
+export default function GlobalSearch(_props: PluginProps): React.ReactElement {
+  const router = useRouter();
+  const [keyword, setKeyword] = useState("");
+  const [open, setOpen] = useState(false);
+
+  const { data } = useGlobalSearch(keyword, 8);
+
+  const handleSelect = (item: SearchResult): void => {
+    const base = TYPE_PATH_MAP[item.type] ?? "/search";
+    router.push(`${base}/${item.id}`);
+    setOpen(false);
+    setKeyword("");
+  };
+
+  const results = data ?? [];
+
+  return (
+    <div className="relative">
+      <input
+        type="search"
+        value={keyword}
+        onChange={(e) => {
+          setKeyword(e.target.value);
+          setOpen(true);
+        }}
+        onFocus={() => setOpen(true)}
+        placeholder="搜索学生、班级、考试…"
+        aria-label="全局搜索"
+        className="w-72 rounded-button border border-rule bg-surface px-sm py-xs text-small text-ink"
+      />
+      {open && keyword.length > 0 ? (
+        <ul className="absolute right-0 z-50 mt-sm w-72 rounded-card border border-rule bg-surface p-sm shadow-md">
+          {results.length === 0 ? (
+            <li className="text-small text-ink-muted">暂无结果</li>
+          ) : (
+            results.map((item) => (
+              <li key={`${item.type}-${item.id}`}>
+                <button
+                  type="button"
+                  onClick={() => handleSelect(item)}
+                  className="flex w-full flex-col border-b border-rule py-xs text-left"
+                >
+                  <span className="text-small text-ink">{item.title}</span>
+                  <span className="text-tiny text-ink-muted">
+                    {item.subtitle}
+                  </span>
+                </button>
+              </li>
+            ))
+          )}
+        </ul>
+      ) : null}
+    </div>
+  );
+}