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/d3-timer/src/timeout.js

@@ -0,0 +1,11 @@
+import {Timer} from "./timer.js";
+
+export default function(callback, delay, time) {
+  var t = new Timer;
+  delay = delay == null ? 0 : +delay;
+  t.restart(elapsed => {
+    t.stop();
+    callback(elapsed + delay);
+  }, delay, time);
+  return t;
+}