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/isJSON.d.mts

@@ -0,0 +1,32 @@
+//#region src/predicate/isJSON.d.ts
+/**
+ * Checks if a given value is a valid JSON string.
+ *
+ * A valid JSON string is one that can be successfully parsed using `JSON.parse()`. According to JSON
+ * specifications, valid JSON can represent:
+ * - Objects (with string keys and valid JSON values)
+ * - Arrays (containing valid JSON values)
+ * - Strings
+ * - Numbers
+ * - Booleans
+ * - null
+ *
+ * String values like `"null"`, `"true"`, `"false"`, and numeric strings (e.g., `"42"`) are considered
+ * valid JSON and will return true.
+ *
+ * This function serves as a type guard in TypeScript, narrowing the type of the argument to `string`.
+ *
+ * @param value The value to check.
+ * @returns Returns `true` if `value` is a valid JSON string, else `false`.
+ *
+ * @example
+ * isJSON('{"name":"John","age":30}'); // true
+ * isJSON('[1,2,3]'); // true
+ * isJSON('true'); // true
+ * isJSON('invalid json'); // false
+ * isJSON({ name: 'John' }); // false (not a string)
+ * isJSON(null); // false (not a string)
+ */
+declare function isJSON(value: unknown): value is string;
+//#endregion
+export { isJSON };