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/compat/util/toPlainObject.d.ts

@@ -0,0 +1,17 @@
+//#region src/compat/util/toPlainObject.d.ts
+/**
+ * Converts value to a plain object flattening inherited enumerable string keyed properties of value to own properties of the plain object.
+ *
+ * @param value The value to convert.
+ * @returns Returns the converted plain object.
+ *
+ * @example
+ * function Foo() {
+ *   this.b = 2;
+ * }
+ * Foo.prototype.c = 3;
+ * toPlainObject(new Foo()); // { b: 2, c: 3 }
+ */
+declare function toPlainObject(value?: any): any;
+//#endregion
+export { toPlainObject };