Tests cover the scenario where mcporter is run in a completely empty
environment (no config files anywhere - not in project dir, home dir,
or env vars). Before the fix, this would crash with ENOENT.
Unit tests:
- resolveConfigPath returns explicit=false when no config exists anywhere
E2E tests:
- list command succeeds with empty environment
- list --json outputs valid JSON with empty servers array
- config list succeeds
- config doctor succeeds and shows version banner
