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/postcss/lib/parse.d.ts

@@ -0,0 +1,9 @@
+import { Parser } from './postcss.js'
+
+interface Parse extends Parser {
+  default: Parse
+}
+
+declare let parse: Parse
+
+export = parse