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/array/flatten.d.mts

@@ -0,0 +1,20 @@
+//#region src/array/flatten.d.ts
+/**
+ * Flattens an array up to the specified depth.
+ *
+ * @template T - The type of elements within the array.
+ * @template D - The depth to which the array should be flattened.
+ * @param arr - The array to flatten.
+ * @param depth - The depth level specifying how deep a nested array structure should be flattened. Defaults to 1.
+ * @returns A new array that has been flattened.
+ *
+ * @example
+ * const arr = flatten([1, [2, 3], [4, [5, 6]]], 1);
+ * // Returns: [1, 2, 3, 4, [5, 6]]
+ *
+ * const arr = flatten([1, [2, 3], [4, [5, 6]]], 2);
+ * // Returns: [1, 2, 3, 4, 5, 6]
+ */
+declare function flatten<T, D extends number = 1>(arr: readonly T[], depth?: D): Array<FlatArray<T[], D>>;
+//#endregion
+export { flatten };