Add settings page for managing forecasting API key and URL via UI

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/node_modules/es-toolkit/dist/fp/array/union.d.ts

@@ -0,0 +1,20 @@
+//#region src/fp/array/union.d.ts
+/**
+ * Creates a function that returns unique values from the piped array and secondArray.
+ *
+ * Values keep their first occurrence order, matching the main {@link union} behavior.
+ * Use the returned function with {@link pipe}.
+ *
+ * @template T - The type of elements in the arrays.
+ * @param secondArray - Values to include after the piped array.
+ * @returns A function that maps a readonly array to its union with secondArray.
+ *
+ * @example
+ * import { pipe, union } from 'es-toolkit/fp';
+ *
+ * pipe([1, 2], union([2, 3]));
+ * // => [1, 2, 3]
+ */
+declare function union<T>(secondArray: readonly T[]): (array: readonly T[]) => T[];
+//#endregion
+export { union };