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/stop-iteration-iterator/index.d.ts

@@ -0,0 +1,7 @@
+declare global {
+    const StopIteration: (object & { readonly __brand__?: unique symbol }) | undefined;
+}
+
+declare function getStopIterationIterator<T>(origIterator: { next(): IteratorResult<T> }): Iterator<T, unknown, T>;
+
+export = getStopIterationIterator;