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/mean.mjs

@@ -0,0 +1,20 @@
+import { sum } from "./sum.mjs";
+//#region src/math/mean.ts
+/**
+* Calculates the average of an array of numbers.
+*
+* If the array is empty, this function returns `NaN`.
+*
+* @param nums - An array of numbers to calculate the average.
+* @returns The average of all the numbers in the array.
+*
+* @example
+* const numbers = [1, 2, 3, 4, 5];
+* const result = mean(numbers);
+* // result will be 3
+*/
+function mean(nums) {
+	return sum(nums) / nums.length;
+}
+//#endregion
+export { mean };