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/isNull.d.ts

@@ -0,0 +1,24 @@
+//#region src/predicate/isNull.d.ts
+/**
+ * Checks if the given value is null.
+ *
+ * This function tests whether the provided value is strictly equal to `null`.
+ * It returns `true` if the value is `null`, and `false` otherwise.
+ *
+ * This function can also serve as a type predicate in TypeScript, narrowing the type of the argument to `null`.
+ *
+ * @param x - The value to test if it is null.
+ * @returns True if the value is null, false otherwise.
+ *
+ * @example
+ * const value1 = null;
+ * const value2 = undefined;
+ * const value3 = 42;
+ *
+ * console.log(isNull(value1)); // true
+ * console.log(isNull(value2)); // false
+ * console.log(isNull(value3)); // false
+ */
+declare function isNull(x: unknown): x is null;
+//#endregion
+export { isNull };