Better scenario variable editing

Some users have gotten confused by the scenario variable editing interface. This change makes the interface easier to understand.

app/vitest.config.ts

@@ -4,6 +4,10 @@ import { configDefaults, defineConfig, type UserConfig } from "vitest/config";
 const config = defineConfig({
   test: {
     ...configDefaults, // Extending Vitest's default options
+    setupFiles: ["./src/tests/helpers/setup.ts"],
+
+    // Unfortunately using threads seems to cause issues with isolated-vm
+    threads: false,
   },
   plugins: [tsconfigPaths()],
 }) as UserConfig;