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.js

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+const require_sumBy = require("./sumBy.js");
+//#region src/math/meanBy.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
+*/
+function meanBy(items, getValue) {
+	return require_sumBy.sumBy(items, (item) => getValue(item)) / items.length;
+}
+//#endregion
+exports.meanBy = meanBy;