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/flattenDeep.d.ts

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+//#region src/array/flattenDeep.d.ts
+/**
+ * Utility type for recursively unpacking nested array types to extract the type of the innermost element
+ *
+ * @example
+ * ExtractNestedArrayType<(number | (number | number[])[])[]>
+ * // number
+ *
+ * ExtractNestedArrayType<(boolean | (string | number[])[])[]>
+ * // string | number | boolean
+ */
+type ExtractNestedArrayType<T> = T extends ReadonlyArray<infer U> ? ExtractNestedArrayType<U> : T;
+/**
+ * Flattens all depths of a nested array.
+ *
+ * @template T - The type of elements within the array.
+ * @param arr - The array to flatten.
+ * @returns A new array that has been flattened.
+ *
+ * @example
+ * const arr = flattenDeep([1, [2, [3]], [4, [5, 6]]]);
+ * // Returns: [1, 2, 3, 4, 5, 6]
+ */
+declare function flattenDeep<T>(arr: readonly T[]): Array<ExtractNestedArrayType<T>>;
+//#endregion
+export { ExtractNestedArrayType, flattenDeep };