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/predicate/isFunction.d.ts

@@ -0,0 +1,17 @@
+//#region src/predicate/isFunction.d.ts
+/**
+ * Checks if `value` is a function.
+ *
+ * @param value The value to check.
+ * @returns Returns `true` if `value` is a function, else `false`.
+ *
+ * @example
+ * isFunction(Array.prototype.slice); // true
+ * isFunction(async function () {}); // true
+ * isFunction(function* () {}); // true
+ * isFunction(Proxy); // true
+ * isFunction(Int8Array); // true
+ */
+declare function isFunction(value: any): value is (...args: any[]) => any;
+//#endregion
+export { isFunction };