Docs(test[smoke]): Add docs-site smoke check

why: Ensure the site test target has at least one passing test.
what:
- Add a minimal vitest smoke test for the docs workspace

Author: tony

astro/packages/site/docs/tests/smoke.test.ts

@@ -0,0 +1,8 @@
+import { buildApiPackage } from '@libtmux/api-model'
+import { describe, expect, it } from 'vitest'
+
+describe('docs site', () => {
+  it('references core api model helpers', () => {
+    expect(typeof buildApiPackage).toBe('function')
+  })
+})