feat(client): 通知中心与未读角标(F16)

- Topbar 增加通知铃铛与未读数
- 新增 /notifications 列表页，支持筛选与标记已读
- 为 workflow/reimbursement/auth 通知提供跳转入口

client/src/api/notifications.ts

@@ -0,0 +1,51 @@
+import { apiRequestData } from "./http";
+
+export type NotificationItem = {
+  id: string;
+  type: string;
+  title: string;
+  body: string | null;
+  targetType: string | null;
+  targetId: string | null;
+  readAt: string | null;
+  createdAt: string;
+};
+
+export type NotificationListResponse = {
+  page: number;
+  pageSize: number;
+  total: number;
+  unreadOnly: boolean;
+  unreadCount: number;
+  items: NotificationItem[];
+};
+
+export type NotificationListQuery = {
+  page?: number;
+  pageSize?: number;
+  unreadOnly?: boolean;
+};
+
+function toQueryString(query: NotificationListQuery) {
+  const params = new URLSearchParams();
+  if (query.page != null) params.set("page", String(query.page));
+  if (query.pageSize != null) params.set("pageSize", String(query.pageSize));
+  if (query.unreadOnly != null) params.set("unreadOnly", query.unreadOnly ? "1" : "0");
+  const qs = params.toString();
+  return qs ? `?${qs}` : "";
+}
+
+export async function fetchNotifications(query: NotificationListQuery = {}) {
+  return apiRequestData<NotificationListResponse>(`/api/notifications${toQueryString(query)}`);
+}
+
+export async function markNotificationRead(notificationId: string) {
+  return apiRequestData<{ id: string; readAt: string | null }>(
+    `/api/notifications/${notificationId}/mark-read`,
+    {
+      method: "POST",
+      body: JSON.stringify({}),
+    },
+  );
+}
+