frontend: don't wait before rendering

The default behaviour of Tanstack Router is to wait at least 500ms
before showing the rendered route, so that the loading spinner doesn't
flicker. We don't want that, as we don't seem to have a working loading
spinner anyway, and this just unnecessarily adds FCP latency.

frontend/src/main.tsx

@@ -33,6 +33,7 @@ const router = createRouter({
   basepath: config.root,
   defaultErrorComponent: GenericError,
   defaultPreload: "intent",
+  defaultPendingMinMs: 0,
   context: { client },
 });