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/flatten.d.ts

@@ -0,0 +1,21 @@
+//#region src/fp/array/flatten.d.ts
+/**
+ * Creates a function that flattens an array up to the specified depth.
+ *
+ * The returned function is lazy-capable inside {@link pipe}. A trailing
+ * short-circuiting operator can stop before later nested values are visited.
+ *
+ * @template T - The type of elements in the array.
+ * @template D - The depth to which nested arrays should be flattened.
+ * @param depth - The flattening depth. Defaults to 1.
+ * @returns A function that maps the piped array to a flattened array.
+ *
+ * @example
+ * import { flatten, pipe } from 'es-toolkit/fp';
+ *
+ * pipe([1, [2, [3]]], flatten(2));
+ * // => [1, 2, 3]
+ */
+declare function flatten<T, D extends number = 1>(depth?: D): (array: readonly T[]) => Array<FlatArray<T[], D>>;
+//#endregion
+export { flatten };