fix: add missing shutil import for Matrix E2EE setup

Cherry-picked from PR #5136 by thakoreh.
setup_gateway() uses shutil.which('uv') at line 2126 but shutil was
never imported at module level, causing NameError during Matrix E2EE
auto-install. Adds top-level import and regression test.

hermes_cli/setup.py

@@ -14,6 +14,7 @@ Config files are stored in ~/.hermes/ for easy access.
 import importlib.util
 import logging
 import os
+import shutil
 import sys
 from pathlib import Path
 from typing import Optional, Dict, Any