chore: update Docker configuration and improve health check functionality

- Added Docker health check endpoint to the FastAPI application, returning a 200 status when the app is running.
- Updated Dockerfile to include curl for health checks and modified entrypoint script to exit on errors.
- Enhanced .dockerignore and .gitignore files to exclude coverage and test artifacts.
- Updated docker-compose.prod.yml to specify version.
- Added pytest-cov as a development dependency to improve test coverage reporting.

tests/test_app.py

@@ -16,6 +16,13 @@ def client():
     return TestClient(app)
 
 
+def test_health(client):
+    """Health endpoint returns 200 and status ok for Docker HEALTHCHECK."""
+    r = client.get("/health")
+    assert r.status_code == 200
+    assert r.json() == {"status": "ok"}
+
+
 def test_duties_invalid_date_format(client):
     r = client.get("/api/duties", params={"from": "2025-01-01", "to": "invalid"})
     assert r.status_code == 400