feat: enhance CSV import functionality, integrate react-query for data fetching, and refactor admin components

frontend/src/queryClient.ts

@@ -0,0 +1,11 @@
+import { QueryClient } from "@tanstack/react-query";
+
+// Central QueryClient instance so utilities (e.g. file upload) can invalidate queries.
+export const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      refetchOnWindowFocus: false,
+      retry: 1,
+    },
+  },
+});