✅(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/__init__.py

@@ -0,0 +1 @@
+"""Tests for the summary service."""

src/summary/tests/api/__init__.py

@@ -0,0 +1 @@
+"""Tests for the API summary service."""

src/summary/tests/api/test_api_health.py

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+"""Integration tests for the health check endpoints."""
+
+
+class TestHeartbeat:
+    """Tests for the /__heartbeat__ endpoint."""
+
+    def test_returns_200(self, client):
+        """The heartbeat endpoint responds with 200 OK without a token."""
+        response = client.get("/__heartbeat__")
+
+        assert response.status_code == 200
+
+
+class TestLBHeartbeat:
+    """Tests for the /__lbheartbeat__ endpoint."""
+
+    def test_returns_200(self, client):
+        """The load-balancer heartbeat endpoint responds with 200 OK without a token."""
+        response = client.get("/__lbheartbeat__")
+
+        assert response.status_code == 200

src/summary/tests/conftest.py

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+"""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)