feat: add admin traffic usage page with TanStack Table

Add AdminTrafficUsage page showing per-user traffic statistics by node
with period filtering (1/3/7/14/30d), server-side sorting, search,
pagination, and CSV export. Uses @tanstack/react-table with manual
sorting and dynamic node columns.

src/api/adminTraffic.ts

@@ -0,0 +1,53 @@
+import apiClient from './client';
+
+export interface TrafficNodeInfo {
+  node_uuid: string;
+  node_name: string;
+  country_code: string;
+}
+
+export interface UserTrafficItem {
+  user_id: number;
+  telegram_id: number | null;
+  username: string | null;
+  full_name: string;
+  tariff_name: string | null;
+  subscription_status: string | null;
+  traffic_limit_gb: number;
+  device_limit: number;
+  node_traffic: Record<string, number>;
+  total_bytes: number;
+}
+
+export interface TrafficUsageResponse {
+  items: UserTrafficItem[];
+  nodes: TrafficNodeInfo[];
+  total: number;
+  offset: number;
+  limit: number;
+  period_days: number;
+}
+
+export interface ExportCsvResponse {
+  success: boolean;
+  message: string;
+}
+
+export const adminTrafficApi = {
+  getTrafficUsage: async (params: {
+    period?: number;
+    limit?: number;
+    offset?: number;
+    search?: string;
+    sort_by?: string;
+    sort_desc?: boolean;
+  }): Promise<TrafficUsageResponse> => {
+    const response = await apiClient.get('/cabinet/admin/traffic', { params });
+    return response.data;
+  },
+
+  exportCsv: async (data: { period: number }): Promise<ExportCsvResponse> => {
+    const response = await apiClient.post('/cabinet/admin/traffic/export-csv', data);
+    return response.data;
+  },
+};