Update Coolify deployment guide to clarify production and development dependencies; refactor import statements for consistency and add requirements-dev.txt for development dependencies.

Co-authored-by: Copilot <copilot@github.com>

frontend/tests/test_frontend.py

@@ -6,7 +6,7 @@ from unittest.mock import MagicMock, patch
 os.environ.setdefault("FLASK_SECRET_KEY", "test-secret")
 os.environ.setdefault("BACKEND_URL", "http://backend-mock")
 
-from frontend.app.main import app  # noqa: E402
+from app.main import app  # noqa: E402
 
 
 @pytest.fixture