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/recharts/es6/util/getEveryNth.js

@@ -0,0 +1,27 @@
+/**
+ * Given an array and a number N, return a new array which contains every nTh
+ * element of the input array. For n below 1, an empty array is returned.
+ * For n equal to 1, the input array is returned as is.
+ * For n greater than the length of the array, an array containing the first element
+ * and every nTh element after that (if any) is returned.
+ *
+ * @param array An input array.
+ * @param n A number specifying which elements to take.
+ * @returns The result array of the same type as the input array.
+ */
+export function getEveryNth(array, n) {
+  if (n < 1) {
+    return [];
+  }
+  if (n === 1) {
+    return array;
+  }
+  var result = [];
+  for (var i = 0; i < array.length; i += n) {
+    var item = array[i];
+    if (item !== undefined) {
+      result.push(item);
+    }
+  }
+  return result;
+}