feat: add customer cart with expiry, shipping addresses with USPS validation, and multi-item PayPal checkout

frontend/src/admin/adminSettingsApi.ts

@@ -0,0 +1,17 @@
+export interface AdminSettings {
+  cartExpiryHours: number;
+}
+
+export async function fetchAdminSettings(): Promise<AdminSettings> {
+  const res = await fetch('/api/admin/settings');
+  return res.json();
+}
+
+export async function updateAdminSettings(settings: AdminSettings): Promise<AdminSettings> {
+  const res = await fetch('/api/admin/settings', {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(settings)
+  });
+  return res.json();
+}