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/join.d.ts

@@ -0,0 +1,20 @@
+//#region src/fp/array/join.d.ts
+/**
+ * Creates a function that joins array values into a string.
+ *
+ * The separator is passed to Array.prototype.join, so undefined uses a comma.
+ * Use the returned function with {@link pipe}.
+ *
+ * @template T - The type of elements in the array.
+ * @param separator - The separator placed between values.
+ * @returns A function that maps a readonly array to a joined string.
+ *
+ * @example
+ * import { join, pipe } from 'es-toolkit/fp';
+ *
+ * pipe(['a', 'b', 'c'], join('-'));
+ * // => 'a-b-c'
+ */
+declare function join<T>(separator?: string): (array: readonly T[]) => string;
+//#endregion
+export { join };