test: exclude e2e/ Playwright specs from the vitest unit run

vitest's default include glob picked up e2e/*.spec.js and crashed
trying to collect Playwright's test() as a vitest test. Unit and e2e
suites run through separate commands (npm test vs npm run test:e2e).

Author: ctkrug

vitest.config.js

@@ -5,5 +5,9 @@ export default defineConfig({
     // jsdom, not the vitest default "node" environment, since main.js and
     // future UI code touch the DOM directly (no framework abstracting it).
     environment: "jsdom",
+    // e2e/ holds Playwright specs, run separately via `npm run test:e2e` —
+    // vitest's default include glob would otherwise try (and fail) to
+    // collect them as unit tests.
+    exclude: ["**/node_modules/**", "e2e/**"],
   },
 });