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/sumBy.js

@@ -0,0 +1,24 @@
+//#region src/math/sumBy.ts
+/**
+* Calculates the sum of an array of numbers when applying
+* the `getValue` function to each element.
+*
+* If the array is empty, this function returns `0`.
+*
+* @template T - The type of elements in the array.
+* @param items - An array to calculate the sum.
+* @param getValue - A function that selects a numeric value from each element.
+*   It receives the element and its zero‑based index in the array.
+* @returns The sum of all the numbers as determined by the `getValue` function.
+*
+* @example
+* sumBy([{ a: 1 }, { a: 2 }, { a: 3 }], (x, i) => x.a * i); // Returns: 8
+* sumBy([], () => 1); // Returns: 0
+*/
+function sumBy(items, getValue) {
+	let result = 0;
+	for (let i = 0; i < items.length; i++) result += getValue(items[i], i);
+	return result;
+}
+//#endregion
+exports.sumBy = sumBy;