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/array/union.d.mts

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+//#region src/array/union.d.ts
+/**
+ * Creates an array of unique values from all given arrays.
+ *
+ * This function takes two arrays, merges them into a single array, and returns a new array
+ * containing only the unique values from the merged array.
+ *
+ * @template T - The type of elements in the array.
+ * @param arr1 - The first array to merge and filter for unique values.
+ * @param arr2 - The second array to merge and filter for unique values.
+ * @returns A new array of unique values.
+ *
+ * @example
+ * const array1 = [1, 2, 3];
+ * const array2 = [3, 4, 5];
+ * const result = union(array1, array2);
+ * // result will be [1, 2, 3, 4, 5]
+ */
+declare function union<T>(arr1: readonly T[], arr2: readonly T[]): T[];
+//#endregion
+export { union };