feat: add test suite for health and root endpoints

- TestClient-based tests: health returns 200 + {"status": "ok"}, POST /health returns 405, GET / returns 200
- conftest.py with shared client fixture
- requirements-test.txt with pytest and httpx

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: baijum

requirements-test.txt

@@ -0,0 +1,2 @@
+pytest>=7.0
+httpx>=0.24.0

tests/__init__.py

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+import pytest
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+
+@pytest.fixture
+def client():
+    return TestClient(app)

tests/conftest.py

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+def test_root_returns_200(client):
+    response = client.get("/")
+    assert response.status_code == 200

tests/test_app.py

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+def test_health_returns_200(client):
+    response = client.get("/health")
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok"}
+
+
+def test_health_post_not_allowed(client):
+    response = client.post("/health")
+    assert response.status_code == 405