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/percentile.js

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+//#region src/math/percentile.ts
+/**
+* Calculates the value at the given percentile of an array of numbers.
+*
+* Sorts the array in ascending order and returns the element at the nearest rank.
+* See {@link https://en.wikipedia.org/wiki/Percentile#The_nearest-rank_method | Nearest rank method}.
+*
+* `NaN` values are sorted as the smallest values. Returns `NaN` if the array is empty.
+*
+* @param arr - An array of numbers to calculate the percentile.
+* @param percentile - The percentile to compute, in the range `[0, 100]`.
+* @returns The value at the given percentile.
+* @throws {Error} Throws an error if `percentile` is not a number, less than `0`, or greater than `100`.
+*
+* @example
+* percentile([1, 2, 3, 4, 5], 50);
+* // Returns 3
+*
+* @example
+* percentile([1, 2, 3, 4, 5], 75);
+* // Returns 4
+*
+* @example
+* percentile([5, 1, 4, 2, 3], 0);
+* // Returns 1
+*/
+function percentile(arr, percentile) {
+	if (Number.isNaN(Number(percentile))) throw new Error(`Expected percentile to be a number but got "${percentile}".`);
+	if (percentile < 0) throw new Error(`Expected percentile to be >= 0 but got "${percentile}".`);
+	if (percentile > 100) throw new Error(`Expected percentile to be <= 100 but got "${percentile}".`);
+	if (arr.length === 0) return NaN;
+	const sorted = arr.slice().sort((a, b) => {
+		return (Number.isNaN(a) ? Number.NEGATIVE_INFINITY : a) - (Number.isNaN(b) ? Number.NEGATIVE_INFINITY : b);
+	});
+	if (percentile === 0) return sorted[0];
+	return sorted[Math.ceil(sorted.length * (percentile / 100)) - 1];
+}
+//#endregion
+exports.percentile = percentile;