test(infra): add vitest smoke test

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/smoke.test.ts

@@ -0,0 +1,7 @@
+import { describe, it, expect } from 'vitest';
+
+describe('smoke', () => {
+  it('runs', () => {
+    expect(1 + 1).toBe(2);
+  });
+});