refactor: restrict WikiTree integration to the apps.wikitree.com domain and add helper utilities

src/util/wikitree_util.ts

@@ -0,0 +1,17 @@
+/**
+ * Base URL for Topola Viewer hosted on apps.wikitree.com.
+ * WikiTree API calls only work when the app is served from this domain.
+ */
+export const WIKITREE_TOPOLA_URL =
+  'https://apps.wikitree.com/apps/wiech13/topola-viewer';
+
+/**
+ * Returns true if the app is currently hosted on the apps.wikitree.com domain.
+ *
+ * WikiTree's API requires being served from this domain due to authentication
+ * and CORS restrictions. When not on this domain, WikiTree data loading does
+ * not work.
+ */
+export function isOnWikitreeDomain(): boolean {
+  return window.location.hostname === 'apps.wikitree.com';
+}