✅(summary) add minimal test suite for health endpoint

Based on cameldev's work, introduce basic tests to ensure the
health endpoint responds correctly.

src/summary/tests/conftest.py

@@ -0,0 +1,12 @@
+"""Integration test configuration. Provides shared fixtures."""
+
+import pytest
+from fastapi.testclient import TestClient
+
+from summary.main import app
+
+
+@pytest.fixture()
+def client():
+    """Provide a FastAPI TestClient for integration tests."""
+    return TestClient(app)