chore: ruff autofix — import sorting, remove unused imports

Mechanical cleanup via `ruff check --fix` + `ruff format`:
- cli.py, test_auth.py: import sorting (isort convention)
- cli.py: remove unused AuthenticationError import in _run_setup
- config.py: remove unused `field` import
- test_auth.py: remove unused MagicMock import
- test_config.py: remove unused Path import

No functional change. All 131 tests remain green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_auth.py

@@ -1,9 +1,10 @@
 """Tests for auth.py."""
 
-import pytest
-from unittest.mock import AsyncMock, MagicMock, patch
+from unittest.mock import AsyncMock, patch
 
-from mcp_synology_container.auth import AuthManager, AuthenticationError
+import pytest
+
+from mcp_synology_container.auth import AuthenticationError, AuthManager
 from mcp_synology_container.config import AppConfig, ConnectionConfig