tests: a hung test now fails instead of hanging forever

`node --test` has no timeout by default. Two revert-checks left runs wedged on
session.test.js for forty minutes with no output and no way to tell from the
outside whether they were working or stuck.

app/package.json

@@ -4,7 +4,7 @@
   "type": "module",
   "description": "Dev-only. Users never run npm: the app is served as plain ES modules with no build step.",
   "scripts": {
-    "test": "node --test",
+    "test": "node --test --test-timeout=30000",
     "test:layout": "playwright test",
     "test:all": "npm test && npm run test:layout"
   },