test(server): disable file parallelism to avoid CI failures

apps/server/vite.config.mts

@@ -16,6 +16,7 @@ export default defineConfig(() => ({
       provider: 'v8' as const,
       reporter: [ "text", "html" ]
     },
+    fileParallelism: false,
     pool: "threads"
   },
 }));