Fix API keys list not showing — unwrap .keys from response

Backend returns { keys: [...] } but frontend was treating the whole
object as the array, so apiKeys.length was always falsy.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Settings.tsx

@@ -5760,7 +5760,8 @@ const ApiKeysPage: React.FC = () => {
     queryFn: async () => {
       const response = await fetch('/forecasting/api/config/api-keys')
       if (!response.ok) throw new Error('Failed to fetch API keys')
-      return response.json()
+      const data = await response.json()
+      return data.keys
     },
   })