Add getAppSettings API function

src/shared/api/appSettings.ts

@@ -0,0 +1,27 @@
+import type { ApiClient } from "./client.js";
+
+export interface AppSettingsFilterOptions {
+  searchFrom?: string;
+  searchTo?: string;
+  timeStep?: string;
+}
+
+export interface AppSettingsResponse {
+  showDebugVersion?: string;
+  uiOptions?: {
+    isTestVersion?: string;
+    filter?: {
+      onlineboard?: AppSettingsFilterOptions;
+      schedule?: AppSettingsFilterOptions;
+    };
+    buttons?: Record<string, unknown>;
+  };
+}
+
+/**
+ * Fetch the global UI configuration from the backend. Includes date range
+ * limits for online-board and schedule searches.
+ */
+export async function getAppSettings(client: ApiClient): Promise<AppSettingsResponse> {
+  return client.get<AppSettingsResponse>("/appSettings");
+}