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/math/meanBy.d.mts

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+//#region src/math/meanBy.d.ts
+/**
+ * Calculates the average of an array of numbers when applying
+ * the `getValue` function to each element.
+ *
+ * If the array is empty, this function returns `NaN`.
+ *
+ * @template T - The type of elements in the array.
+ * @param items An array to calculate the average.
+ * @param getValue A function that selects a numeric value from each element.
+ * @returns The average of all the numbers as determined by the `getValue` function.
+ *
+ * @example
+ * meanBy([{ a: 1 }, { a: 2 }, { a: 3 }], x => x.a); // Returns: 2
+ * meanBy([], x => x.a); // Returns: NaN
+ */
+declare function meanBy<T>(items: readonly T[], getValue: (element: T) => number): number;
+//#endregion
+export { meanBy };