Add/expand tests for normalize (39%→97%), searcher (39%→100%),
layers (28%→97%), split_mega_files (34%→72%).
Fix mcp_server.py parse_args→parse_known_args to prevent SystemExit
when imported during pytest (CI was crashing on all test jobs).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>