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/math/add.d.ts

@@ -0,0 +1,19 @@
+//#region src/compat/math/add.d.ts
+/**
+ * Adds two numbers while safely handling `NaN` values.
+ *
+ * This function takes two numbers and returns their sum. If either of the numbers is `NaN`,
+ * the function returns `NaN`.
+ *
+ * @param value - The first number to add.
+ * @param other - The second number to add.
+ * @returns The sum of the two numbers, or `NaN` if any input is `NaN`.
+ *
+ * @example
+ * const result1 = add(2, 3);    // result1 will be 5
+ * const result2 = add(5, NaN);  // result2 will be NaN
+ * const result3 = add(NaN, 10); // result3 will be NaN
+ */
+declare function add(value: number, other: number): number;
+//#endregion
+export { add };