fix: address Copilot review — remove unused imports, isolate HOME in tests, restore dev extra

tests/test_mcp_server.py

@@ -8,13 +8,10 @@ via monkeypatch to avoid touching real data.
 
 import json
 
-import pytest
-
 
 def _patch_mcp_server(monkeypatch, config, palace_path, kg):
     """Patch the mcp_server module globals to use test fixtures."""
     from mempalace import mcp_server
-    import chromadb
 
     monkeypatch.setattr(mcp_server, "_config", config)
     monkeypatch.setattr(mcp_server, "_kg", kg)