test: add unit test suite for config, health checks, and lifespan wiring

tests/unit/test_healthz.py

@@ -0,0 +1,11 @@
+import pytest
+from httpx import AsyncClient
+
+pytestmark = [pytest.mark.unit, pytest.mark.asyncio]
+
+
+async def test_healthz_returns_ok_status(client: AsyncClient) -> None:
+    response = await client.get("/healthz")
+
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok"}