- Drop unused StreamingResponse import from app/nodes.py (will be
re-added in Task 2 when the SSE endpoint is implemented)
- Replace em dash with colon in _get_ollama_url HTTPException detail
- Remove unused os and unittest.mock imports from test_nodes.py
(mock imports will return in Task 2 tests)
- Create app/nodes.py with _CONFIG_DIR testability seam, _load_config,
_profiles_dir, _profile_path, _load_profile, _get_ollama_url helpers,
and stub list_nodes endpoint returning [] when no coordinator_url is set
- Mount nodes router at /api/nodes-mgmt in app/api.py
- Add profiles_dir comment to config/label_tool.yaml.example cforch section
- Create tests/test_nodes.py with autouse fixture and two passing tests
