feat: import broker portfolio JSON

frontend/src/api/portfolio.ts

@@ -0,0 +1,6 @@
+import type { ImportPortfolioResponse, PortfolioFile } from '@family-budget/shared';
+import { api } from './client';
+
+export function importPortfolio(data: PortfolioFile): Promise<ImportPortfolioResponse> {
+  return api.post('/api/import/portfolio', data);
+}