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/predicate/isSymbol.d.ts

@@ -0,0 +1,18 @@
+//#region src/compat/predicate/isSymbol.d.ts
+/**
+ * Check whether a value is a symbol.
+ *
+ * This function can also serve as a type predicate in TypeScript, narrowing the type of the argument to `symbol`.
+ *
+ * @param value The value to check.
+ * @returns Returns `true` if `value` is a symbol, else `false`.
+ * @example
+ * isSymbol(Symbol.iterator);
+ * // => true
+ *
+ * isSymbol('abc');
+ * // => false
+ */
+declare function isSymbol(value: any): value is symbol;
+//#endregion
+export { isSymbol };