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/isWellBehavedNumber.js

@@ -0,0 +1,6 @@
+export function isWellBehavedNumber(n) {
+  return Number.isFinite(n);
+}
+export function isPositiveNumber(n) {
+  return typeof n === 'number' && n > 0 && Number.isFinite(n);
+}