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/array/flattenDeep.mjs

@@ -0,0 +1,18 @@
+import { flattenDepth } from "./flattenDepth.mjs";
+//#region src/compat/array/flattenDeep.ts
+/**
+* Recursively flattens array.
+*
+* @template T
+* @param array - The array to flatten.
+* @returns Returns the new flattened array.
+*
+* @example
+* flattenDeep([1, [2, [3, [4]], 5]]);
+* // => [1, 2, 3, 4, 5]
+*/
+function flattenDeep(value) {
+	return flattenDepth(value, Infinity);
+}
+//#endregion
+export { flattenDeep };