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/flatMapDeep.mjs

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+import { flattenDeep } from "./flattenDeep.mjs";
+//#region src/array/flatMapDeep.ts
+/**
+* Recursively maps each element in an array using a provided iteratee function and then deeply flattens the resulting array.
+*
+* @template T - The type of elements within the array.
+* @template U - The type of elements within the returned array from the iteratee function.
+* @param arr - The array to flatten.
+* @param iteratee - The function that produces the new array elements. It receives the element, its index, and the array.
+* @returns A new array that has been flattened.
+*
+* @example
+* const result = flatMapDeep([1, 2, 3], n => [[n, n]]);
+* // [1, 1, 2, 2, 3, 3]
+*/
+function flatMapDeep(arr, iteratee) {
+	return flattenDeep(arr.map((item, index) => iteratee(item, index, arr)));
+}
+//#endregion
+export { flatMapDeep };