fix: add missing PurchaseOrder type import to api client

frontend/lib/api.ts

@@ -1,4 +1,4 @@
-import type { AnalysisHistoryItem, AnalysisResult, CompanyProfile, Tender } from "./types";
+import type { AnalysisHistoryItem, AnalysisResult, CompanyProfile, Tender, PurchaseOrder } from "./types";
 
 const API_BASE = process.env.NEXT_PUBLIC_API_BASE ?? "";