fix build

Author: aster-void

routes/game/+page.svelte

@@ -1,10 +1,11 @@
 <script lang="ts">
+import { browser } from "$app/environment";
 import { page } from "$app/state";
 import GameLoader from "@/components/GameLoader.svelte";
 import { stages } from "@/stages";
 
 const stageDefinition = $derived(
-  stages.get(page.url.searchParams.get("stage") ?? ""),
+  browser ? stages.get(page.url.searchParams.get("stage") ?? "") : undefined,
 );
 </script>