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>

src/mcp_synology_container/cli.py

@@ -43,8 +43,8 @@ def setup(verbose: bool) -> None:
 
 async def _run_setup() -> None:
     """Interactive setup flow."""
-    from mcp_synology_container.auth import AuthManager, AuthenticationError
-    from mcp_synology_container.config import AppConfig, ConnectionConfig, CONFIG_PATH, save_config
+    from mcp_synology_container.auth import AuthManager
+    from mcp_synology_container.config import CONFIG_PATH, AppConfig, ConnectionConfig, save_config
     from mcp_synology_container.dsm_client import DsmClient, SynologyError
 
     click.echo("=== mcp-synology-container setup ===\n")
@@ -198,7 +198,7 @@ def check(config_path: str | None, verbose: bool) -> None:
 
 async def _run_check(config_path: str | None) -> bool:
     """Run connectivity check. Returns True on success."""
-    from mcp_synology_container.auth import AuthManager, AuthenticationError
+    from mcp_synology_container.auth import AuthenticationError, AuthManager
     from mcp_synology_container.config import load_config
     from mcp_synology_container.dsm_client import DsmClient, SynologyError