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/temp-dir/index.d.ts

@@ -0,0 +1,18 @@
+/**
+Get the real path of the system temp directory.
+
+@example
+```
+import * as os from 'os';
+import tempDirectory = require('temp-dir');
+
+console.log(tempDirectory);
+//=> '/private/var/folders/3x/jf5977fn79jbglr7rk0tq4d00000gn/T'
+
+console.log(os.tmpdir());
+//=> '/var/folders/3x/jf5977fn79jbglr7rk0tq4d00000gn/T' // <= Symlink
+```
+*/
+declare const tempDirectory: string;
+
+export = tempDirectory;