feat: project skeleton with health endpoint

tests/test_health.py

@@ -0,0 +1,9 @@
+from fastapi.testclient import TestClient
+from chat.app import app
+
+
+def test_health_endpoint_returns_ok():
+    client = TestClient(app)
+    response = client.get("/health")
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok"}